Neurogenetics User Manual 2007/2008 Page 1 of 24
Neurogenetics Unit
User Manual 2007-2008
Neurogenetics User Manual 2007/2008 Page 2 of 24
1. Neurogenetics Unit 3-6
Service provision/ DNA test...
Neurogenetics User Manual 2007/2008 Page 3 of 24
The Neurogenetics Unit is situated wit...
Neurogenetics User Manual 2007/2008 Page 4 of 24
Episodic ataxia type 2 (CACNA1A)
Familial Amyloid Polyneuropathy (TTR).
Neurogenetics User Manual 2007/2008 Page 5 of 24
Epsiodic ataxia type 2 (CACNA1A): 4 months
Familial Amyloid Polyneuropath...
Neurogenetics User Manual 2007/2008 Page 6 of 24
This is the most recently identified gene and a single base pair mis-sens...
Neurogenetics User Manual 2007/2008 Page 7 of 24
with a very high sensitivity and specificity. The analysis looks for the ...
Neurogenetics User Manual 2007/2008 Page 8 of 24
Huntington’s Disease (autosomal dominant inheritance) is the commonest ca...
Neurogenetics User Manual 2007/2008 Page 9 of 24
Other diseases that may present with chorea with additional extrapyramida...
Neurogenetics User Manual 2007/2008 Page 10 of
5. NHNN Genetic Guide to genetic testing for dystonia
Dr Sarah Tabrizi
Neurogenetics User Manual 2007/2008 Page 11 of
simplest classification system is neurophysiological and divides CMT int...
Neurogenetics User Manual 2007/2008 Page 12 of
Using neurophysiology and a family history it is usually possible to cla...
Neurogenetics User Manual 2007/2008 Page 13 of
Genetic testing in AD or sporadic CMT2:
1. Screen MFN2.
2. If MFN 2 nega...
Neurogenetics User Manual 2007/2008 Page 14 of
mutations. RAB7 is not available for routine screening. In patients with...
Neurogenetics User Manual 2007/2008 Page 15 of
Clinical type Inh...
Neurogenetics User Manual 2007/2008 Page 16 of
Charcot-Marie-Tooth type 2 autosomal dominant (CMT 2 / HMSN II)
CMT 2A A...
Neurogenetics User Manual 2007/2008 Page 17 of
Neurogenetics User Manual 2007/2008 Page 18 of
Neurogenetics User Manual 2007/2008 Page 19 of
A systematic programme for MD complications screening exists in the musc...
Neurogenetics User Manual 2007/2008 Page 20 of
If a dominant pedigree is identified it is worth considering the gene te...
Neurogenetics User Manual 2007/2008 Page 21 of
First test Second test Third test
Myotonic dystrophy DM1 DM2
Neurogenetics User Manual 2007/2008 Page 22 of
In a non-LHON patient if no mutations are detected in blood the gold sta...
Neurogenetics User Manual 2007/2008 Page 23 of
Skeletal Muscle channelopathies
First test Second test Third test
Neurogenetics User Manual 2007/2008 Page 24 of
Episodic Ataxias and Familial Hemiplegic migraine
First test Second test...
Upcoming SlideShare
Loading in...5



Published on

  • Be the first to comment

  • Be the first to like this

No Downloads
Total Views
On Slideshare
From Embeds
Number of Embeds
Embeds 0
No embeds

No notes for slide


  1. 1. Neurogenetics User Manual 2007/2008 Page 1 of 24 Neurogenetics Unit NHNN/ION User Manual 2007-2008
  2. 2. Neurogenetics User Manual 2007/2008 Page 2 of 24 CONTENTS Page 1. Neurogenetics Unit 3-6 Staff Service provision/ DNA tests available Samples required Consent Target response times 2. Genetic tests in Parkinson’s disease and Parkinsonism 7 3. Genetic tests in inherited ataxias 8 4. Genetic tests in Huntington’s disease and choreiform disorders 10 5. Genetic tests in dystonia 13 6. Genetic tests in inherited neuropathies 14 7. Genetic tests in muscle disease and Ion channel disease 22
  3. 3. Neurogenetics User Manual 2007/2008 Page 3 of 24 1. NEUROGENETICS UNIT: USER MANUAL The Neurogenetics Unit is situated within the Department of Molecular Neuroscience at the Institute of Neurology. Included in the unit is the Neurogenetics Laboratory of the National Hospital for Neurology and Neurosurgery/University College London Hospital. The laboratory is CPA accredited and provides a regional, national and international diagnostic service for inherited neurological disorders. This manual is designed to give guidance to users for currently available DNA service tests and is correct as of January 2008. It is updated annually. Staff Consultant Neurologists Professor N.W. Wood, PhD, FRCP, FMedSci Professor M.G. Hanna, MD, FRCP Dr. M.M. Reilly, MD, FRCPI Dr. S. Tabrizi, PhD, MRCP Dr H Houlden PhD, MRCP Clinical Nurse Specialists Ms. R. Taylor, RGN MSc Mr Colm Treacy RGN Clinical scientists Dr. M.B. Davis, PhD, FRCPath Ms. A Haworth, MSc, FRCPath Ms. M.G. Sweeney, BSc, DipRCPath Dr. W. Wakeling, PhD, DipRCPath Dr. V. Gibbons, PhD Dr. R. Labrum, PhD Ms. C. Woodward, BSc Pre-registration Scientists Dr. S. Pemble, PhD Dr R Sud PhD Mr J Polke BSc Genetic Technologist Ms. E. Mudanohwo Mr J. Hehir Mr B Phillimore Office Manager Ms. N. Boateng Service provision-Laboratory contact number 0845 155 5000 ext 724250 Diagnostic, predictive and prenatal genetic tests are carried out when clinically appropriate. Informed consent is required. Diagnostic tests will be carried out for outside hospitals when appropriate clinical details and evidence of consent accompany the sample. Predictive and prenatal tests will only be carried out for individuals who have been seen in a genetic clinic either at the NHNN or at a regional clinical genetics centre. Enquires concerning the clinical indications for genetic testing should be addressed to Professor Wood (movement disorders including Parkinson’s disease and cerebellar ataxias), Professor Hanna (muscle disease, mitochondrial, ion channel), Drs M Reilly/H Houlden (peripheral nerve) or Dr Tabrizi (Huntington’s disease) Enquires concerning the range of tests are available, type of sample required, analytical procedures and result interpretation should be addressed to Dr MB Davis (ext 724282), Ms MG Sweeney or Ms A Haworth (ext 724266). Information and consent forms are available from Ms N Boateng (ext 724250). Result enquiries should be addressed to ext 724250. If this extension is unmanned a message should be left on the answer phone and enquiries will be dealt with as soon as possible. Tests available: Autosomal dominant cerebellar ataxias (SCA1, SCA2, SCA3, SCA6, SCA7, SCA12, SCA17). Andersen Syndrome (KCNJ2) Dentatorubropallidoluysian Atrophy (DRPLA). Dopa Responsive Dystonia (GCH1). Episodic ataxia type 1 (KCNA1)
  4. 4. Neurogenetics User Manual 2007/2008 Page 4 of 24 Episodic ataxia type 2 (CACNA1A) Familial Amyloid Polyneuropathy (TTR). Finnish Type Amyloidosis (Gelsolin) Familial British Dementia (BRI). Familial Hemiplegic Migraine (CACNA1A). Friedreich's Ataxia (FRDA). Frontal lobe temporal dementia (MAPT, TAU). Known family mutations only. Hereditary Motor and Sensory Neuropathy (chromosome 17p11.2 duplication, CX32, MPZ, MFN2, GDAP1). Hereditary Neuropathy with Liability to Pressure Palsy (chromosome 17p11.2 deletion, PMP22). Hereditary Sensory Neuropathy (SPTLC1) Huntington's disease (HD). Junctophillin (JPH3) Leber's Hereditary Optic Neuropathy (LHON). Mitochondrial Myopathies (MM). Myotonia Congenita (CLCN1). Paramyotonia Congenita (SCN4A). Parkinson’s disease (PARK2, PARKIN, LRRK2 G2019S) Periodic paralysis (SCN4A, CACNA1S). Primary Torsion Dystonia (DYT1). X linked Bulbospinalneuronopathy (XLBSN). The laboratory is also willing to confirm research results for other disorders in individual cases. Testing will then be available to other family members. For availability of other tests in UK genetic labs please see Service developments: DNA from individuals with disorders for which tests are not currently available may be sent for storage, pending future analysis. Details of current developments are available from the laboratory. Sample required: For genetic analysis, we request at least two mls blood, in two PLASTIC EDTA tubes. Clinical details, family history and where possible a detailed pedigree should be supplied. Samples from wards and clinics at the NHNN should be accompanied by a yellow analysis request form. Blood and DNA samples from outside hospitals can be sent by first class mail. Tissue samples e.g. muscle, should be sent frozen, on dry ice, by courier. Please advise the laboratory of the arrival of these samples in advance. CVS samples are not accepted except by prior arrangement. Consent: Consent is required for all genetic tests. For samples originating within the NHNN, clear indication of consent, for diagnostic and/or research purposes must be completed on the request form. Samples referred from other laboratories must be sent with written consent or a clear indication that consent has been obtained. Samples received into the laboratory without this information will be stored without analysis until consent is obtained. Target report times: Tests available within the Neurogenetics laboratory: Urgent referrals All predictive and prenatal tests: 2 weeks Diagnostic tests with acute clinical need: 2 weeks Non urgent referrals Autosomal dominant cerebellar ataxias (SCA1, SCA2, SCA3, SCA6, SCA7, SCA12, SCA17): 8 weeks Andersen Syndrome (KCNJ2): 4 months Dentatorubropallidoluysian Atrophy (DRPLA): 8 weeks Dopa Responsive Dystonia (GCH1): 4 months Episodic ataxia type 1 (KCNA1): 4 months
  5. 5. Neurogenetics User Manual 2007/2008 Page 5 of 24 Epsiodic ataxia type 2 (CACNA1A): 4 months Familial Amyloid Polyneuropathy (TTR): 4 months Finnish Type Amyloidosis (Gelsolin) :8 weeks Familial British Dementia (BRI): 8 weeks Familial Hemiplegic Migraine (CACNA1A): 4 months Friedreich's Ataxia (FRDA): 8 weeks Frontal lobe temporal dementia (MAPT, TAU). Known family mutations only: 8 weeks Hereditary Motor and Sensory Neuropathy: chromosome 17p duplication; 8weeks HMSN point mutation analysis: Connexin-32 (GJB3), GDAP1, MPZ, MFN2: 4 months Hereditary Liability to Pressure Palsy: 8 weeks Hereditary Sensory Neuropathy (SPTLC1): 4 months Huntington's disease (HD): 8 weeks Leber's Hereditary Optic Neuropathy (LHON): 8 weeks Mitochondrial Myopathies (MM): 8 weeks/4 months depending on analysis required Myotonia Congenita (CLCN1): 4 months Paramyotonia Congenita (SCN4A): 4 months Parkinson’s disease (PARK2, PARKIN, PARK8, LRRK2:G2019S): 4 months Periodic paralysis (SCN4A, CACNA1S): 4 months Primary Torsion Dystonia (DYT1): 8 weeks X linked Bulbospinalneuronopathy (XLBSN): 8 weeks Where a report will not be available within the stated time, the referring clinician will be contacted as soon as possible. External referrals: Report times are determined by the receiving laboratory: the Neurogenetics laboratory will forward the report to the referring clinician as soon as it is available. Report enquiries may be made to the Neurogenetics Unit. Charges: 2007/2008 Charges for provider to provider and private referrals are available from the Neurogenetics laboratory. 2. NHNN GUIDE TO GENETIC TESTING FOR PARKINSON'S DISEASE AND PARKINSONISM Professor Nicholas Wood Parkinson's disease and parkinsonism is a commonly occurring akinetic rigid syndrome. The last few years have seen a dramatic change in our understanding of the genetic bases of these disorders. PARKINSON’S DISEASE Parkinson's disease although classically thought of as a non-genetic disease, it is now clear that a significant sub-group of patients do have primary mendelian mutation. Currently there are 5 genes which are widely accepted as being associated with a phenotype compatible with classical Parkinson's disease. Two of these, alpha-synuclein and LRRK2, are inherited in autosomal dominant fashion. Three, Parkin, DJ1 and PINK1 are autosomal recessively inherited. These bare facts relating to the mode of inheritance however, do not tell the full story. For instance, the emerging story of LRRK2 is now associated with reduced penetrance, thereby gene carriers may be unaffected and a clear autosomal dominant family history may not be obvious. There is also accumulating but unproven evidence that single hit mutations in the recessive genes may well contribute to an individual’s parkinsonian syndrome. Therefore, giving guidance on gene testing is complicated. It is generally too early to give precise estimates of the relative burdens of these mutations. However a few facts can be stated: • Alpha- synuclein (SCNA or Park1) Mutations in alpha-synuclein are incredibly rare and this is not currently being offered as a service. • LRRK2 (aka Dardarin or Park8)
  6. 6. Neurogenetics User Manual 2007/2008 Page 6 of 24 This is the most recently identified gene and a single base pair mis-sense mutation (G2019S) has been shown to be found commonly in both familial and apparently sporadic disease. • DJ1 (Park7) This is a rare autosomal recessive condition and this is not yet available in service. • PINK1 (Park6) Mutations in PINK1 appear to be more common than DJ1 but still relatively rare, this is not yet in service. • Parkin (Park2) Numerically, worldwide mutations in the parkin gene have been found most frequently of all the Parkinson’s genes. The range of mutations is wide and includes mis-sense, nonsense and a number of gene rearrangements. The genetic analysis is complex and we are currently able to offer direct sequencing of exons in this gene and dosage analysis for rearrangements. It should be noted, however, that most patients in outbred populations such as the UK are compound heterozygotes, i.e. they have a different mutation on each allele. PARKINSONISM Complicated parkinsonism such as MSA and PSP generally do not appear to have a high recurrence risk and no gene tests are indicated in clinically typical cases. However, in the case of familial or unusual syndromes, which may include earlier age of onset, consideration for sequencing of the TAU gene in cases of PSP as well as complicated fronto-temporal dementia parkinsonism is suggested. DOPA RESPONSIVE DYSTONIA This may sometimes present as young onset parkinsonian syndrome with or without dystonia. For details of genetic testing please see section on dystonia. SPINO CEREBELLAR ATAXIA Some of the complicated dominant ataxias, particularly SCAs 1, 2 and 3 may be complicated by extra-pyramidal syndromes including parkinsonism. In selected cases, such as those with a family history, or parkinsonism complicated by ataxia, it may be worthwhile considering SCA gene mutation. For details, please see section on ataxias. OTHERS There are a number of other rare neurodegenerative disease which may present with parkinsonian features (e.g. Pank2, Wilson’s disease). If a genetic analysis is being considered please contact the laboratory for advice as to the availability of such tests. 3. NHNN GENETIC GUIDE TO INHERITED ATAXIAS Professor Nicholas Wood and Dr Paola Giunti Ataxia may be found in a variety of clinical situations. There are a large number of genetic causes, but a few basic rules can be recognised. If a degenerative ataxia is being considered, the age of onset is important. Generally speaking, onset below the age of 20 years is very likely to be autosomal recessive. Onset over the age of 25 conversely, is very likely to be autosomal dominant. X-linked forms of ataxia are very rare and when present are usually extremely complicated and other clues such as aetiology is given by the clinical presentation and other investigations. Mitochondrial DNA mutation may also give rise to ataxia, but again this is usually a complicated picture, including such features as pigmentary retinopathy, epilepsy, etc. These are discussed under the section on mitochondrial diseases. Autosomal recessive ataxias The commonest of these is Friedreich's ataxia. This has a distinctive clinical phenotype encompassing progressive gait and limb ataxia, pyramidal signs and a neuropathy predominantly of sensory type. Genetic testing for this is a relatively straightforward matter
  7. 7. Neurogenetics User Manual 2007/2008 Page 7 of 24 with a very high sensitivity and specificity. The analysis looks for the presence of an expansion in intron 1 of the Frataxin gene. The vast majority of patients have an abnormal expansion on both alleles but approximately 2-4% has a single expansion and a point mutation. The analysis performed in the NHNN diagnostic laboratory will only pick up the expansion. Therefore, if no expansion is found, this effectively excludes the diagnosis of Friedreich's ataxia as to date; there are still no reports of two point mutations being found in a single individual. If, however, a single expansion is found, this has 2 possible explanation: that it is the cause of the patient’s ataxia and the second allele carries a point mutation (detectable by sending the sample to an outside laboratory); or it represents the carrier frequency in the general population of about 1 in 120. Therefore a clinical decision must be made and if requested we can send the DNA away for sequencing to look for the point mutation. There are a number of other rare ataxic syndromes including ataxia telengiectasia and ataxia associated with ocular motor apraxia (AOA1 & 2). These can be also assessed in appropriately selected cases by Professor Malcolm Taylor Cancer Research Institute University of Birmingham. Although rare, perhaps the most important ataxia not to be missed in this group is an ataxia associated with Vitamin E deficiency. This is due to mutations in the alpha tocopherol transporting protein. This is not offered as a genetic service but as the diagnosis is readily reached by measuring Vitamin E this does not hamper diagnostic accuracy. Although rare, it is potentially treatable or at least modifiable by Vitamin E supplementation and therefore should be considered in appropriate cases. There are a number of other rarer syndromes which may present with ataxia including: A variant of Tay Sachs due to hexosaminidase A deficiency, this is usually complicated by a predominantly motor neuronopathy. A newly described tremor ataxia syndrome associated with presence of the permutation of the fragile X gene (FXTAS). Rarely Niemann Pick type C can present with an early onset complicated ataxia picture. Vertical gaze abnormalities are usually present. Autosomal dominant ataxias Slightly confusingly there are 2 classification systems which can be viewed in parallel. The clinical classification based on Anita Harding’s work in the early 1980s, describes three sub- groups of autosomal dominant cerebellar ataxia (ADCA). Type 1 was complicated by a variety of additional feature including some but not necessarily all of the following: neuropathy, dementia, extrapyramidal features, and optic atrophy. Type 2 was complicated by a maculopathy and Type 3 was relatively pure. This is still clinically useful and can guide the relevant genetic analysis. The genetic classification for the SpinoCerebellar Ataxias (SCAs) is based on the order in which the chromosomal location of the causative gene was identified. At the time of writing, the number of SCAs is approximately 30. In not all of these has the gene been identified and even when the gene has been identified, not all are available as a diagnostic service. Routine diagnostic services at NHNN involves genes SCAs 1,2,3,6,7, 12 and 17. SCA7 counts for virtually all the cases of the Type 2 form of ADCA, namely that associated with a maculopathy. This is the rarest of the gene tests. SCAs 1, 2 and 3 account for approximately 50% of ADCA Type 1 and SCA6 accounts for approximately 50% of the pure type. This is generally speaking a later onset disease and more slowly progressive than the others. Therefore it can be seen that in 50% or perhaps a little over, cases of ataxia with a dominant family history SCA testing on the currently available list will identify the mutation. We can also offer on special request SCA12 and 17 which are much rarer. As clinical clues, SCA12 is associated with prominent tremor and SCA17 may present with a complicated ataxia with chorea and can even look a bit like Huntington's disease. We are not currently offering the other SCAs at this time. SCA14 is currently being offered on a research basis by colleagues in Oxford (Dr Kevin Talbot) and in selected cases we can arrange for samples to be sent for analysis to Dr Talbot. However, as with all research-based results, unless these are then validated in a CPA approved laboratory we advise most strongly against communicating these to patients and their family. 4. NHNN GENETIC GUIDE TO GENETIC TESTING FOR CHOREIFORM DISORDERS Dr Sarah Tabrizi Huntington’s Disease
  8. 8. Neurogenetics User Manual 2007/2008 Page 8 of 24 Huntington’s Disease (autosomal dominant inheritance) is the commonest cause of inherited chorea in the UK, therefore with a choreiform patient where the cause is clearly not acquired - this should be the first genetic test. There is not always a positive family history although this should always be asked for. The implications for other family members of a positive diagnostic test for HD should also always be discussed and please refer for advice if any questions regarding this. Clinical features of HD Common motor abnormalities such as chorea are seen in 90% of adult onset cases of HD. Also think of Huntington’s Disease if patients present with a combination of dystonia, parkinsonism, bradykinesia - as HD may present with an akinetic rigid form particularly in young adults or juvenile cases. In a young person (<20y) presenting with a parkinsonian syndrome, juvenile Huntington’s Disease should be tested for. Patients with Huntington’s Disease commonly have oculomotor disturbance characterised by delayed initiation of saccades, slowing saccades and head thrusting to initiate saccades. Pursuit is impaired and there may be evidence of gaze impersistence. Patients have impairment of voluntary motor function, dysarthria, dysphagia and cognitive and psychiatric problems are common. Huntington’s Disease may also present with multiple tics, predominant psychiatric symptoms or predominant cognitive symptoms in a frontal/subcortical pattern. DRPLA DRPLA (autosomal dominant) is rare in Europe and the United States; however, it does present with a number of clinical phenotypes for which the gene may be tested for. It can present with a Huntington’s Disease phenocopy with an identical picture to Huntington’s disease. In young onset patients, particularly under the age of 30y, it tends to present with a progressive myoclonic epilepsy-picture with more marked dementia than is seen in patients with Huntington’s Disease. In patients with later onset typically above the age of 30y, DRPLA typically presents with a milder phenotype with ataxia, mild chorea and milder cognitive impairment. Gene Testing for Huntington’s Disease phenocopies A number of diseases can present with clinical features very similar to Huntington’s Disease, and these may be tested for in the Neurogenetics laboratory, if the Huntington’s Disease and DRPLA gene tests are negative. Other inherited causes of HD phenocopies are: Inherited prion diseases which may be tested for by analysing the open reading frame of the prion gene. This is undertaken by Professor John Collinge’s team, and this is done as a free research-based service. Spinocerebellar ataxia (SCA) types1, 2, 3 and 17 may all present like Huntington’s Disease. Neuro-acanthocytosis (AD or AR) and neuro-ferritinopathy may present like Huntington’s Disease. However, genetic testing for these disorders is expensive and not easily available. HDL-2 (due to mutations in the Junctophillin 3 gene) although this has only been described in people of North African origin to date. Other causes of inherited chorea that may present with features similar to Huntington’s Disease, but with additional neurological symptoms are Neuro-acanthocytosis as mentioned above, but repeated blood films are a useful test for this; Macleod syndrome which is X-linked with mutations in the XK gene (these patients typically have acanthocytes on peripheral blood film, a high CK and their red blood cells have weak expression of Kell system antigens due to no expression of XK protein); and benign hereditary chorea. There are genes available for these, but are not currently testable on a service basis in the UK. Mitochondrial disorders may mimic many neurodegenerative disorders, and these can be tested via the Neurogenetics laboratory. Other inherited choreiform disorders
  9. 9. Neurogenetics User Manual 2007/2008 Page 9 of 24 Other diseases that may present with chorea with additional extrapyramidal features that we can test for in the Neurogenetics laboratory are Wilson’s disease (autosomal recessive due to mutations in a copper transport ATP’ase), Friedreich’s ataxia (autosomal recessive due to intronic GAA repeat mutation in the FRDA gene), Neuro-degeneration with brain iron accumulation (autosomal recessive due to PANK2 mutations), Ataxia Telangectasia (autosomal recessive disorder due to mutations in the AT mutation gene), and Neuroferritinopathy (autosomal dominant due to mutations in the ferritin light chain). In summary and practical advice on what tests to ask for: Of the above gene tests summarised the ones that are important to be aware of and may be tested for in the Neurogenetics lab without discussion are Huntington’s Disease, DRPLA, and SCA 17 (in that order) in patients presenting with Huntington’s disease-like/choreiform clinical phenotypes. Patients with SCA 1,2 and 3 may present with this phenotype but testing for these mutations in this group of patients should be discussed with the Neurogenetics laboratory. All the other genetics tests mentioned should only be asked for and will only be undertaken after discussion with the Neurogenetics team for patients that present with a choreiform disorder. HD TESTING FLOW DIAGRAM
  10. 10. Neurogenetics User Manual 2007/2008 Page 10 of 24 5. NHNN Genetic Guide to genetic testing for dystonia Dr Sarah Tabrizi Dystonias are a heterogeneous group of disorders which are known to have a strong inherited basis. Genetic testing is available for DYT1 (primary torsion dystonia) or DRD (dopa responsive dystonia). DYT1 associated dystonia: Mutations in the DYT1 gene have been associated with autosomal dominant early onset idiopathic torsion dystonia. This typically develops first in the arm or leg in middle to late childhood and progresses to generalised dystonia within about 5 years. Patients are intellectually normal and have no other neurological abnormalities. Although onset is more typical in childhood or early adulthood, it has been described in middle life. There is marked clinical variability in DYT1-associated dystonia ranging from children who are profoundly disabled, to adults who carry this autosomal dominantly inherited gene and have no symptoms. This indicates that the gene is transmitted with reduced penetrance. The DYT1 mutation is caused by a GAG deletion in the protein encoding torsin A. This can be tested for in patients with the appropriate dystonic phenotype in the Neurogenetics laboratory without discussion. Dopa Responsive Dystonia: Dopa Responsive Dystonia (DRD) is characterised by dystonia, concurrent or subsequent parkinsonism, diurnal worsening of symptoms in 75% of cases and a dramatic therapeutic response to Levodopa. Women are affected 2-4 times more frequently than men. Dystonia is the most common presentation and maybe the only feature, however, in childhood DRD may present with a phenotype resembling spastic paraparesis, whereas in adulthood it can present with a phenotype similar to spastic paraparesis or a parkinsonian syndrome. In view of the wide spectrum of symptoms and age of onset, the diagnosis of DRD may be missed and it is widely recommended that all patients with an extrapyramidal motor disorder or individual symptoms within the spectrum of DRD be given a trial of Levodopa. DRD is usually inherited as an autosomal dominant trait with incomplete penetrance. It is due to mutations in the gene encoding GTP-cyclohydrolase 1. There are many different mutations that are found in GCH 1; these can be tested for in the Neurogenetics laboratory. However, before sending off for testing for the DRD gene, it is recommended that the patient has been given and had a good response to Levodopa; a phenylalanine loading test, and CSF examination which may reveal low concentrations of dopamine and serotonin metabolites, neopterin, biopterin and GTP-CH1 activity, all of which can be tested in the metabolic laboratory in the National Hospital for Neurology and Neurosurgery. Other dystonic syndromes: There are currently 15 loci associated with inherited dystonia. An important one to be aware of is the myoclonus/dystonia syndrome which is characterised by a myoclonic/dystonic syndrome which is alcohol-responsive in some patients. This is autosomal dominant with incomplete penetrance and caused by mutations in the gene encoding epsilon-sarcoglycan. Dystonia is also associated with many other syndromes, mainly the heredo-degenerative dystonias, and these will be covered under the sections encompassing choreiform disorders and parkinsonian disorders. 6. NHNN GUIDE TO DNA-BASED DIAGNOSIS IN PATIENTS WITH SUSPECTED HEREDITARY NEUROPATHIES Dr Mary M. Reilly The hereditary neuropathies are a clinically and genetically a heterogeneous group of disorders. Although there are many genetic diseases in which the peripheral nervous system is involved, by far the most important of these is Charcot-Marie-Tooth disease (CMT), which affects 1 in 2,500 of the population. This disease is characterised clinically by distal wasting and weakness, distal sensory loss, hyporeflexia and a variable amount of foot deformity. The
  11. 11. Neurogenetics User Manual 2007/2008 Page 11 of 24 simplest classification system is neurophysiological and divides CMT into type 1 (median motor conduction velocity (MCV) < 38 m/s) and type 2 (median MCV > 38 m/s) although an intermediate form (median MCV 25 – 45 m/s) is increasingly recognised. Clinically it is often difficult to distinguish some forms of CMT2 from some forms of the Hereditary Sensory and Autonomic Neuropathies (HSAN) as will be discussed below. It is not uncommon for patients with CMT to have no sensory symptoms and occasionally no sensory signs which can make the distinction from distal Hereditary Motor Neuronopathy (dHMN) difficult clinically but clear using neurophysiology. Therefore it is necessary to consider CMT, HSAN and dHMN together in determining an approach to the diagnosis of these conditions. Hereditary neuropathy with liability to pressure palsies (HNPP) is genetically related to CMT1A and also needs to be considered under the genetic neuropathies. There are now at least 28 genes that cause CMT (Table 1), 5 genes that cause dHMN (Table 2) and 5 genes that cause HSAN (Table 3). Despite the major advances in identifying the causative genes for these genetic neuropathies only a few of these are available as routine tests (see below) and if these are not present it is usually appropriate that the patient is seen in the peripheral nerve genetic clinic for further evaluation. Patients should always have a detailed clinical evaluation including family history done before genetic testing is considered. In most situations as detailed below, it is appropriate to evaluate the patients neurophysiologically (NCS) before proceeding to genetic testing. In specific circumstances (detailed below) nerve biopsy is indicated. All other inherited neuropathies are rare and appropriate testing should either be discussed with Dr. Reilly or the patient should be referred to her peripheral nerve genetic clinic. Availability of genetic testing in peripheral nerve disease varies in different parts of the UK and this guide will outline what is available in the NHNN with reference to some tests which can be done elsewhere in the UK. General approach to inherited neuropathies (CMT, HNPP, HSAN, dHMN) The first step is to assess if the neuropathy is hereditary. This is crucial as inflammatory neuropathies such as chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) are an important differential as they are treatable. The hereditary nature of the neuropathy may be obvious from the family history but in sporadic cases, a long history, the presence of foot deformity, the lack of positive sensory symptoms or in the case of CMT1, the uniform slowing of the MCV may point to the neuropathy being hereditary. If the neuropathy is hereditary, neurophysiology will help both distinguish CMT from dHMN and also differentiate CMT1 from CMT2. It may be possible to work out the inheritance pattern in clinic but the families are often small making this difficult. The general steps to diagnosing a hereditary neuropathy are: 1. Establish using family history +/- clinical pattern whether the neuropathy is likely to be hereditary. Attempt clinically to differentiate between CMT, HNPP, HSAN and dHMN. 2. Use neurophysiology to distinguish CMT from dHMN. 3. In the case of CMT use neurophysiology to classify CMT into types 1, 2 or intermediate. 4. Use neurophysiology to support clinical diagnosis of HNPP. 5. Occasionally in young children with CMT clinically it is justifiable to screen the Chromosome 17 duplication before neurophysiology is undertaken. 6. Occasionally in family members where an index case has a genetic diagnosis, it is reasonable to proceed to genetic testing without doing neurophysiology. 7. If there is any doubt about the neuropathy being genetic and an inflammatory basis is being considered, a nerve biopsy or referral to the peripheral nerve clinic may be appropriate. 8. Occasionally in young severely affected patients nerve biopsy may be considered early specifically to rule out a treatable cause of the neuropathy. Charcot-Marie-Tooth disease (CMT)
  12. 12. Neurogenetics User Manual 2007/2008 Page 12 of 24 Using neurophysiology and a family history it is usually possible to classify CMT into type 1 or type 2 and to attempt to define the inheritance pattern. CMT1 For CMT1, whether it is autosomal dominant (AD) or sporadic, it is always appropriate to screen the chromosome 17 duplication (containing the peripheral myelin protein 22 gene (PMP-22)) first as it accounts for 70% of CMT1 in the UK. Some of the apparent sporadic cases of CMT1 have an early onset severe phenotype and would have been called Dejerine Sottas disease (DSD) or Congenital Hypomyelinating Neuropathy (CHN) previously. It is now known that most cases of DSD and CHN are due to de novo mutations in the causative genes for AD CMT1. In AD or sporadic CMT1, if the chr. 17 duplication is negative and there is no definite evidence of male to male transmission, connexin 32 (CX32) should be screened next. If CX32 is negative or there is male to male transmission then myelin protein zero (P0) should be screened. If this is negative PMP-22 can be screened but this is not done at NHNN. In appropriate circumstances after discussion with Dr. Reilly, PMP-22 can be sent elsewhere in the UK to be screened. All other causes of AD CMT1 are very rare and not available routinely. At this stage it is appropriate to refer patients to the peripheral nerve genetic clinic (PN genetic clinic). Genetic testing in AD or sporadic CMT1: 1. Chr. 17 duplication. 2. If Chr. 17 negative and there is no ♂ to ♂ transmission screen CX32. 3. If CX32 negative or there is ♂ to ♂ transmission screen P0. 4. If P0 negative, discuss PMP-22 screening with Dr. Reilly. 5. If PMP-22 negative consider referring to the PN genetic clinic. AR CMT1 may be difficult to diagnose clinically unless there is consanguinity or affected siblings. It is often useful to examine the parents clinically and electrophysiologically. Currently the only tests routinely available are screening of P0 and PMP-22. Mutations in both of these genes can cause AD, AR and de novo CMT1. If these are negative it is appropriate to consider referral to the PN genetic clinic. Genetic testing in AR CMT1: 1. Screen P0. 2. If P0 is negative discuss PMP-22 sequencing with Dr. Reilly. 3. If P0 and PMP-22 are negative consider referral to the PN genetic clinic. CMT2 Most cases of CMT2 present with a clear history of AD inheritance or as apparent sporadic cases. It is important in apparent sporadic cases to consider acquired neuropathies as neurophysiology (which is reasonably good at differentiating genetic causes of a demyelinating neuropathy from acquired causes) is not good at differentiating genetic causes of an axonal neuropathy from acquired causes. In AD or sporadic CMT2, the first gene which should be screened is Mitofusin 2 (MFN2) which accounts for approximately 20% of cases of AD CMT2. MFN2 mutations can also occur de novo so consider testing this gene is sporadic cases as well. If MFN2 screening is negative, P0 should be screened as P0 mutations can cause CMT2 as well as CMT1. These are the only genes routinely screened in CMT2 and if they are negative referral to the PN genetic clinic should be considered although there are a few useful phenotype pointers to individual genes that may help the clinician including including a predominant sensory neuropathy with sensory complications seen in CMT2B associated with RAB7 mutations and much greater upper limb (hand) than lower limb wasting and weakness in CMT2D associated with GARS mutations (Table 1.)
  13. 13. Neurogenetics User Manual 2007/2008 Page 13 of 24 Genetic testing in AD or sporadic CMT2: 1. Screen MFN2. 2. If MFN 2 negative, screen P0. 3. If P0 negative consider referral to the PN genetic clinic. There are no genes routinely screened for AR CMT2 so referral to the PN genetic clinic should be considered in these patients. Intermediate CMT This term has been recently in favour to describe patients or families with intermediate conduction velocities. It is particularly useful in recognising patients with x-linked CMT due to CX32 mutations. In a family if the males have a demyelinating neuropathy and the females an axonal neuropathy CX32 should be very high on the list of causes. Also in an individual patient if the MCVs in some nerves are in the demyelinating range and in other nerves in the axonal range CX32 should also be considered. This is important as occasionally these patients have been diagnosed erroneously with CIDP. Hereditary Neuropathy with Liability to Pressure Palsies (HNPP) Patients with HNPP often present with a typical history of recurrent pressure palsies but this condition is underdiagnosed and the most important part of the diagnosis is considering the condition. The crucial clinical point is that all patients with HNPP have widespread NCS abnormalities even if they only have one nerve involved clinically. It is therefore only appropriate to screen these patients genetically after NCS have shown widespread conduction abnormalities. The condition is usually AD but occasionally occurs de novo and is caused by a deletion of the same 1.4 megabase section of chromosome 17 as is duplicated in CMT1A. When suspected the Chr. 17 deletion should be initially screened followed by PMP- 22 sequencing (after discussion with Dr. Reilly) as PMP-22 mutations can rarely cause HNPP. Genetic testing in HNPP: 1. Screen the chr. 17 deletion. 2. If chr. 17 deletion negative discuss PMP-22 sequencing with Dr. Reilly. Distal Hereditary Motor Neuronopathy / Spinal Muscle Atrophy (dHMN / dSMA) Distal Hereditary Motor Neuronopathy also known as distal Spinal Muscle Atrophy (dHMN / dSMA) can be very difficult to distinguish clinically from CMT2 and used to be called spinal CMT. Neurophysiology is essential to distinguish dHMN from CMT2 as there are no sensory abnormalities in dHMN and there will always be at least electrical evidence of sensory involvement in CMT2. There are no genes routinely available for screening for dHMN but as can be seen in tables 1 and 2, many of the recently described causative genes for dHMN have also been described to cause rare forms of CMT2 further confusing the issue. It is appropriate to consider referring these patients to the PN genetic clinic. Genetic testing in dHMN: 1. Consider referral to the PN genetic clinic Hereditary Sensory and Autonomic Neuropathy (HSAN) / Hereditary Sensory Neuropathy (HSN) As some of the HSANs do not have significant autonomic involvement, these particular variants should be more appropriately called HSNs. The cardinal clinical feature is marked sensory involvement with sensory complications such as skin ulcerations, Charcot joints, osteomyelitis, amputations etc. Some of the more rare AR forms present with congenital insensitivity to pain (Table 3.). The commonest form in the UK is HSAN I / HSN I which is an AD mainly sensory neuropathy although there can be significant motor involvement with time. The causative gene for this is serine palmitoyl transferase long chain base subunit 1 (SPTLC1) and all UK patients to date have been found to have one mutation (C133W) with a common founder. This mutation is available as a routine test and as part of the screen exons 5 and 6 are also screened but complete SPTLC1 screening is not available. The clinical presentation of patients with HSAN I due to SPTLC1 mutations is very similar to the patients presenting with CMT2B and RAB7 mutations described above except unusually for a genetic neuropathy there is a high incidence of spontaneous neuropathic pain with SPTLC1
  14. 14. Neurogenetics User Manual 2007/2008 Page 14 of 24 mutations. RAB7 is not available for routine screening. In patients with the phenotype of HSAN 1 and a family history SPTLC1 should be screened. Genetic testing in HSAN / HSN: 1. In AD HSAN I / HSN I screen SPTLC1. 2. If SPTLC1 is negative and in all other forms of HSAN / HSN consider referral to the PN genetic clinic. 3. Familial Amyloid Polyneuropathy (FAP) Of all the other hereditary neuropathies referred to above the only one for which routine testing is available in NHNN is familial amyloid polyneuropathy (FAP). The most common form of FAP is AD and is due to mutations in transthyretin (TTR). This is an extremely important diagnosis to make as liver transplantation is currently considered in all patients and in appropriate patients can be a very useful treatment. The clinical picture is of a sensory motor neuropathy often initially involving the small sensory fibers and presenting with pain, an autonomic neuropathy, cardiac involvement and a variable involvement of other organs such as the eye with vitreous deposits. This diagnosis should especially be considered in patients of Irish or Portuguese descent but can occur in any ethnic group. Genetic testing in FAP: 1. Screen TTR. 2. If negative consider referral to the PN genetic clinic.
  15. 15. Neurogenetics User Manual 2007/2008 Page 15 of 24 TABLE 1: CLASSIFICATION OF CHARCOT-MARIE-TOOTH DISEASE Clinical type Inheritance Locus / Gene 1. Demyelinating (CMT 1) CMT 1A AD Duplication 17p11.2-12 / PMP-22 17p11.2-12 / Point mutation PMP-22 CMT 1B AD 1q22-q23 / Point mutation Po CMT 1C AD 16p13.1 - p12.3 / SIMPLE / LITAF CMT 1D AD 10q21-q22 / Point mutation EGR2 Charcot-Marie-Tooth type 1 x-linked (CMT 1X) CMT 1X X-linked Xq13.1 / Point mutation Cx32 Dejerine-Sottas disease (HMSN III) DSD A AD (AR) 17p11.2-12 / Point mutation PMP-22 DSD B AD (AR) 1q22-q23 / Point mutation Po DSD C AD 10q21-q22 / Point mutation EGR2 Congenital hypomyelinating neuropathy (CHN) CHN A AD 17p11.2-12 / Point mutation PMP-22 CHN B AD 1q22-q23 / Point mutation Po CHN C AD (AR) 10q21-q22 / Point mutation EGR2 Hereditary neuropathy with liability to pressure palsies (HNPP) HNPP A AD Deletion 17p11.2 / PMP-22 17p11.2-12 / Point mutation PMP-22 Charcot-Marie-Tooth type 1 autosomal recessive (CMT1 AR) CMT1 ARA (CMT4A) AR 8q13 - 21.1/ GDAP1 CMT1 ARB1 (CMT4B1) AR 11q22 / MTMR2 CMT1 ARB2 (CMT4B2) AR 11p15 / MTMR13 CMT1 ARC (CMT 4C) AR 5q23-q33 / KIAA1985 CMT1 ARD (CMT4D / HMSNL) AR 8q24 / NDRG1 CMT1 ARE (CCFDN) AR 18q CMT1 ARF (CMT4F) AR 19q13.1-13.3 / Periaxin CMT1 ARG (HMSNR) AR 10q22-q23 2. Axonal (CMT 2)
  16. 16. Neurogenetics User Manual 2007/2008 Page 16 of 24 Charcot-Marie-Tooth type 2 autosomal dominant (CMT 2 / HMSN II) CMT 2A AD 1p35 – p36 / KIF1Bβ AD / GTPase mitofusin 2 CMT 2B AD 3q13 – q22 / RAB7 CMT 2C AD 12q23 – q24 CMT 2D AD 7p14 / GARS CMT 2E AD 8p21 / NF-L CMT 2F AD 7q11-q21 / HSP 27 CMT 2G AD 12q12-q13.3 CMT 2L AD 12q24 / HSP 22 CMT 2 AD 1q22-q23 / Point mutation Po CMT 2 (HMSNP) AD 3q13.1 Charcot-Marie-Tooth type 2 x-linked (CMT 2X) CMT 2X X-linked Xq24 – q26 Charcot-Marie-Tooth type 2 autosomal recessive (CMT2 AR) CMT2 AR AR 1q21.2 – 21.3 / LMNA CMT2 AR AR 19q13.1 CMT2 AR AR 8q21 / GDAP1 TABLE 2: DISTAL HEREDITARY MOTOR NEURONOPATHY (DISTAL HMN / DISTAL SMA) HMN I unknown HMN II 12q24 / HSP 22 HMN II / CMT2F 7q11-q21 / HSP 27 HMN III unknown HMN IV unknown HMN V / CMT 2D 7p / GARS HMN V / Silver syndrome 11q12-q14 / BSCL2 HMN VI SMARD1 / IGHMBP2 HMN VII 2q14
  17. 17. Neurogenetics User Manual 2007/2008 Page 17 of 24 TABLE 3. HEREDITARY SENSORY AND AUTONOMIC NEUROPATHIES Clinical ty pe Inheritance Locus / Gene HSAN I / HSN1 CMT2B HSAN I HSAN IB AD AD AD AD 9q22.1-22.3 / SPTLC1 3q13-q22 / RAB7 unknown 3p22-24 HSAN II HSAN II AR AR 12p13.33 / HSN2 unknown HSAN III AR 9q31-q33 / IKAP HSAN IV AR 1q21-q22 / TRKA HSAN V HSAN V HSAN V AR AR AR 1q21-q22 / TRKA 1p11.2-p13.2 / NGFB unknown
  18. 18. Neurogenetics User Manual 2007/2008 Page 18 of 24 7. NHNN GENETIC GUIDE TO DNA-BASED DIAGNOSIS IN PATIENTS WITH SUSPECTED GENETIC MUSCLE AND CHANNEL DISEASES Dr Michael Hanna Approximately 50% of patients with muscle disease have a genetic cause. New genes for muscle diseases are being found on a regular basis and there is a bewildering array of muscle disease now shown to have a clear single gene genetic basis. Although genetic testing is increasingly useful in achieving a precise diagnosis, there are situations in which a genetic test should not be the first investigation selected. Availability of genetic testing in muscle disease varies in different parts of the UK and this guide will outline what is available at NHNN. An approach to achieve efficient diagnosis in this patient group is outlined below. In those situations where genetic testing should be considered there is often a hierarchy of test selection based on likelihood of positivity. In patients with suspected genetic muscle disease, DNA tests are only ever one part of a thorough diagnostic assessment which is always based upon detailed clinical assessment, careful family history and the informed selection of additional tests including muscle biopsy, specialised neurophysiology and metabolic testing. Informed written consent is essential for all genetic tests. Furthermore, the requesting clinician should consider in advance how and by whom, genetic counseling will be give if the genetic test is positive. At the first consultation with a patient with suspected genetic muscle disease it should always be possible to devise an efficient sequence of investigations that will usually lead to an accurate diagnosis. In those muscle diseases where a genetic test should be the first test selected, it is usually not necessary to simultaneously arrange an EMG and muscle biopsy. It is generally better to await the genetic result, since if it is positive, these tests will be avoided. An important principle when assessing any patient with muscle disease is always to consider whether it is possible that the patient may have an inflammatory muscle disease. If there is a realistic possibility of such a disease early muscle biopsy is very important. The investigational approach to the major genetic muscle diseases and the ion channel diseases is outlined in the text and tables below. Muscular Dystrophies Myotonic Dystrophy Myotonic dystrophy is the commonest form of muscle dystrophy seen in the adult population. It is a dominant multisystem disease affecting skeletal muscle, cardiac muscle, brain and the endocrine system. Distal muscle weakness, myotonia, cataracts and a myopathic facies usually raise suspicion of the diagnosis in typical cases. However, atypical presentations with cognitive impairment, weight loss and cardiac arrhythmias are recognised. Genetic anticipation is a prominent feature in many myotonic dystrophy families. If the diagnosis is suspected the first test is a genetic test for the MD-1 gene. [chr 19] If this is positive the diagnosis is confirmed and further diagnostic tests are not required. If EMG is readily available this may be done as part of the diagnostic testing to confirm myotonia, but if myotonia evident clinically EMG is not essential and the diagnosis can rely on genetic testing for DM1. If DM1 testing is negative consideration should be given to Proximal Myotonic Myopathy – PROMM. Although there are many clinical similarities between PROMM and MD eg the myopathic facies and cataracts there are important distinguishing features. PROMM patients have proximal weakness and myotonia [the myotonia is therefore often difficult to detect clinically] also prominent muscular pain is common in PROMM. Genetic testing is now available for PROMM-the DM2 gene on Chr 3 If DM1 and DM2 are negative it is usually necessary to consider more detailed neurophysiological tests to assess the possibility of a skeletal muscle channelopathy and to proceed to a muscle biopsy
  19. 19. Neurogenetics User Manual 2007/2008 Page 19 of 24 A systematic programme for MD complications screening exists in the muscle clinic and referral should be considered. Fascioscapulohumoral Muscular Dystrophy-FSHD FSHD is dominant dystrophy with 95% penetrance at age 25y and a negligible new mutation rate. The typical phenotype is usually easy to diagnose clinically and includes myopathic weakness of facial, periscapular, peri-humeral and anterior tibial musculature. Muscle weakness is often asymmetric and in some cases may be very mild-eg asymmetric mild scapula winging. In a small proportion of cases the facials muscles may be spared. The gene for FSHD has not been identified. A truncation of a repeat non-coding DNA sequence on chromosome 4q35 has been shown to associate with the disease in around 95% of cases. If this truncation is identified it is generally regarded as confirming a diagnosis of FSHD. It is important to note that if this test is negative it does not necessarily exclude the diagnosis since patients with 4q35 linked disease may not have the truncation and also because there is likely to be a second FSHD gene not yet discovered. The genetic test should be the first test requested. In the majority of cases it is appropriate to await the results of the genetic test and only if negative to proceed with a muscle biopsy and emg. A prominent inflammatory infiltrate is a recognised feature in biopsies from patients with genetically confirmed FSHD. Occasionally patient present with a very high ck >1000. This may cause difficulty in distinguishing from polymyositis. If there is significant weakness and a high CK it is sensible practice to proceed to muscle biopsy and even to commence a course of steroids while waiting for the genetic test result. Emery Dreifuss Muscular Dystrophy Patients have a scapulo-humero-peroneal distribution of muscle weakness. Prominent contracture is an early clinical feature and is typical of EDMD. For this reason EDMD is often classified as one of the “contractural muscle phenotypes”. The contractures are usually an early feature of the muscle disease often when there is only very minimal muscle weakness. The contractures typically affect the cervical extensor muscles [difficulty flexing neck], the biceps tendon [difficulty extending elbow] and the long finger flexor muscle tendons [difficulty extending fingers and wrists]. Cardiac involvement is important in EDMD usually manifesting as hear block and full cardiac evaluation is essential. The other contractural muscle disease to consider if genetic tests for EDMD are negative is Bethlem myopathy [caused by mutations in the collagen 6 gene-but no genetic test currently available]. Cardiac involvement is not a feature of Bethlem myopathy. EDMD is known to associate with mutations in one of two muscle nuclear envelope proteins emerin [X-linked EDMD] and lamin A/C [AD or AR EDMD]. The X-liked from of EDMD associates with mutations in emerin gene. Emerin gene analysis is not easily available therefore in a male with EDMD the first test is a muscle biopsy with emerin antibody immunostaining which is available at NHNN. If emerin staining is reduced emerin gene analysis can be pursued. If emerin immuno-staining is normal then lamina/C gene analysis should be undertaken. In a female or in a family exhibiting clear dominant inheritance Lamin A/C gene analysis should be the first test. If all above prove negative Bethlem myopathy should be considered and referral to muscle clinic appropriate. Limb Girdle muscular dystrophy In adult males the commonest form of a LGMD presentation is Becker’s muscular dystrophy caused by mutations in the Dystrophin gene on the X-chromosome. In a male presenting with LGMD the first test should be dystrophin gene analysis. If this is negative muscle biopsy for immuno-staining should be undertaken. Non-dystrophin LGMD may be recessive or dominant. The dominant form is extremely rare and it is almost always the case that adult patients with LGMD will have a recessive from of the disease. The number of genes discovered to cause LGMD continues to increase at a steady rate. There are currently 8 genes and one linked locus for the recessive form and 3 genes and 3 linked loci for the dominant form. Most of the known genes responsible for LGMD are very large and gene testing is not easily available and is generally not the first test that should be requested. Generally, once dystrophin gene testing has been completed and if it is negative all LGMD patients should proceed to muscle biopsy for immunostaining which will direct any subsequent genetic investigations
  20. 20. Neurogenetics User Manual 2007/2008 Page 20 of 24 If a dominant pedigree is identified it is worth considering the gene test for Lamin A/C which can occasionally cause dominant LGMD [as well as EDMD above]. At the same time it is reasonable to proceed to a muscle biopsy/emg to confirm a dystrophic process. It should be noted that immunostaining in a dominant muscle disease is generally not useful since it is unusual that the responsible protein will be reduced in quantity in the muscle [in contrast to recessive muscular dystrophies]. Sporadic or recessive pedigrees of LGMD are much more common. It should be noted that although several genes have now been identified in LGMD most of these genes seem to be more relevant to a paediatric age range presentations. The exception to this are LGMD2I caused by mutations in the FKRP gene and LGMD 2B caused by mutations in the Dysferlin gene. FKRP gene testing is more easily available and can be requested early ie before muscle biopsy but dysferlin gene analysis is not easily available and muscle biopsy is the first test. Suspect dysferlin if the ck is very high in adult usually .>5000 Summary LGMD In a male Becker’s commonest-first test is Dystrophin then biopsy Dominant LGMD extremely rare-first test Lamin A/C gene and biopsy Recessive LGMD-most of the genes discovered relevant to paediatric not adult practice – exceptions are FKRP and dysferlin. Gene test is available for FKRP but not for Dysferlin where muscle biopsy is the first test. Oculopharyngeal muscular dystrophy This is a rare dominant muscular dystrophin but with a characteristic phenotype and an available gene test. Occasional recessive families are described. It enters into the differential diagnosis of mitochondrial CPEO and ocular pharyngeal predominant myasthenia. It is typically a late onset >45 years disease and often begins with dysphagia followed by ptosis and eventually ophthalmoplegia. Tongue atrophy may develop. There may be neck flexor and extensor muscle weakness. Later in the disease there may be proximal limb weakness usually mild to moderate. Dominant and recessive OPMD is caused by a stable short (GCG)7-13 on chromosme 14. Gene tests is the first investigation-if negative muscle biopsy and EMG. However, because of concerns about myasthenia early EMG is often appropriate. Muscular Dystrophies
  21. 21. Neurogenetics User Manual 2007/2008 Page 21 of 24 First test Second test Third test Myotonic dystrophy DM1 DM2 Biopsy/emg/Muscle clinic FSHD 4q35 rearang FKRP Biopsy Emery Dreifuss Male Muscle biopsy/emg Emerin gene Lamin A/C Muscle clin Female Lamin A/C geneMuscle biopsy/emg Muscle clin Limb girdle MD Dominant Lamin A/C geneMuscle biopsy/emg Muscle clin Recessive FKRP gene Muscle biopsy/emg Muscle clin X-linked/Spor Dystrophin gene Muscle biopsy/emg Muscle clin OPMD PABP2 gene Muscle biopsy/emg Muscle clin Metabolic Muscle Disease Mitochondrial Respiratory Chain Diseases A wide range of clinical phenotypes are recognised to occur in association with mitochondrial respiratory chain dysfunction. Initially the majority of genetically defined phenotypes had mutations in mitochondrial DNA, but now it is increasingly recognised that mutations in nuclear encoded genes can cause respiratory chain dysfunction resulting in neurological disease. It is now evident that all forms of inheritance [Dominant, recessive, X-linked, maternal and sporadic] are possible in mitochondrial respiratory chain disease depending on the genetic basis. In practice it remains the case that the available genetic tests for mitochondrial diseases are mtDNA tests. It should be emphasised that the routinely available mtDNA tests are relatively limited. Although there are 16696 nucleotides that make up the mitochondrial genome routinely available service tests only check a handful of these positions. The service tests that are available have been selected on the basis of the frequency with which they cause neurological disease. At present there are no routinely available tests to check for any of the discovered nuclear gene mutations. A mitochondrial respiratory chain disease may be suspected in a number of clinical settings and it is generally helpful to consider splitting up defined phenotypes although in practice there is considerable clinical overlap. Typical phenotypes which are well described in standard reviews are MELAS, MERRF, LHON, myopathy, CPEO and KSS. In practice the diagnosis needs to be considered when their may only be fragments of full clinical syndromes or the patients have elements of a number of different syndromes. Useful pointers to consider are the presence of myopathy, neuropathy or deafness in the context of a complex CNS phenotype. In practice if a mitochondrial respiratory chain disease is suspected it is sensible to select the available mtDNA point mutations to be analysed in a blood sample. These are mutations at positions 3243, 8344 and 8993. In a patient under the age of 30 blood mtDNA deletion analysis can be requested. The hit rate from this limited analysis of blood mtDNA is likely to be very low however, if positive a secure diagnosis of mitochondria disease is achieved without the need for further investigations. In patients with LHON the hit rate from blood analysis is much better. The majority of LHON cases in the UK will have one of the three common point mutations at positions 11778, 14484 or 3460.
  22. 22. Neurogenetics User Manual 2007/2008 Page 22 of 24 In a non-LHON patient if no mutations are detected in blood the gold standard investigations include muscle biopsy and respiratory chain enzymology. The majority of patients with a mitochondrial DNA mutation will have ragged red fibres and/or cytochrome c oxidase negative fibres and/or a measurable defect on mitochondrial respiratory chain enzymology. Furthermore, muscle tissue is a much better tissue to analyse for mtDNA mutations. In particular mitochondrial DNA deletions are much more reliably detectable in muscle compared to blood. If above assessments do not produce a positive result and mitochondrial disease is suspected referral to the muscle clinic should be considered from where access to research based analysis can be considered. Glycogen Storage Diseases Fatty Acid Metabolism Disorders Genetic tests are not the first step when evaluating metabolic muscle diseases associated with disturbed glycogen or fatty acid metabolism. The first tests should always be detailed biochemical evaluation eg ischaemic lactate test, urinary organic acids and acylcarnitine profiles. Muscle biopsy and fibroblast biopsies are commonly needed. Referral to the muscle and or metabolic clinic is suggested Metabolic muscle diseases First test Second test Third test Mitochondrial Myopathy mtDNA muscle biopsy Muscle clinic CPEO blood mtDNA muscle MELAS screen resp chain MERRF Overlap Glycogen Muscle biopsy Muscle/metab clinic Stor disease Metabol tests Eg Mcardle ischaem lact Fatty acid Muscle biopsy Muscle/metab clinic Disorders Skin biopsy Metabol tests Acylcarnitine Urine organ acids Skeletal Muscle Channelopathies The muscle clinic at NHNN is the UK national referral centre for all patients suspected of having a skeletal muscle channelopathy. This includes clinical assessment, DNA diagnosis, molecular expression proof of pathogenicity for new mutations, and genotype specific treatment selection and supervision. Genetic tests have been developed over recent years and in the main now do represent the first test to select in patients suspected of having one of the main skeletal muscle channelopathies namely- Periodic paralysis Paramyotonia congenital Myotonia congenita In practice a same day electrophysiology service allows supporting evidence to be obtained to optimize test selection. Muscle biopsy and provocative tests are now rarely required. If gene tests are negative in suspected cases referral to the muscle clinic is suggested.
  23. 23. Neurogenetics User Manual 2007/2008 Page 23 of 24 Skeletal Muscle channelopathies First test Second test Third test Periodic paralysis SCN4A Specialised EMG Muscle clinic CACNA1S Periodic paralysis Cardiac arrhthm Muscle clinic Dysmorphism KCNJ2 Myotonia congentia CLCN1 Specialised emg Muscle clinic Paramyotonia Cong SCN4A specialised emg Muscle clinic Cong Myaesthenia Muscle clinic Brain channelopathies An increasing number of single gene brain paroxysmal neurological disorders have now been shown to be caused by mutations in genes coding for ion channels. Routine DNA-based diagnostic tests for these disorders remains very limited but expansion of this service is anticipated in the future. Episodic ataxias The episodic ataxias were the first brain channelopathies to be genetically characterised and are uncommon disorders inherited in an autosomal dominant fashion Episodic ataxia type 1 To date only 10 families have been reported or identified in the UK and around 30 world-wide. Patients experience movement or stress induced momentary episodes of profound cerebellar dysfunction. Episodes last no more than a few minutes and may happen multiple times per day. Attacks may cluster. In-between attacks there is persistent neuromyotonia caused by peripheral nerve hyperexcitability. The neuromyotonia may be clinically evident or only detectable by EMG. Some patients are described with isolated neuromyotonia as the only manifestation of mutations in the brain potassium channel KCNA1 [chrom 12] that causes EA1.Gene testing of the brain potassium channel can be arranged by discussion with Dr Hanna and/or referral to the muscle-channel clinic may be considered. Episodic ataxia type 2 EA2 is more common that EA1-there are hundreds of families described worldwide. Attacks are precipitated by emotion or intercurrent illness and are characterized by generalised cerebellar ataxia lasting hours to days. Prominent migraine like headache occurs in 50% of attacks. Over time it is usual that patients develop a fixed cerebellar syndrome which can become significant. Point mutations in the brain calcium channel CACNA1A are causative- There are a large number of mutations distributed throughout this large 48 exon gene. At present only SCA-6 expansion analysis is available as a service. The SCA-6 expansion has occasionally been associated with the EA2 phenotype but more commonly associates with a late onset progressive ataxia. Familial Hemiplegic Migraine There are now three genes reported to cause familial hemiplegic migraine-an ATPase gene, a brain sodium channel and a brain calcium channel. Of these, only calcium channel gene analysis is available as a service test. The commonest point mutation in CACNA1A [T666M] that causes FHM is a routine service test.
  24. 24. Neurogenetics User Manual 2007/2008 Page 24 of 24 Episodic Ataxias and Familial Hemiplegic migraine First test Second test Third test EA2 SCA6 Muscle/channel-clinic EA1 emg Muscle/channel- clinic KCNA1 FHM CACNA1A T666M Muscle/channel clinic