Neuromuscular Genetic Diagnosis


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Reviews some of the simpler diagnoses and how to approach less typical cases, avoiding pitfalls in gene testing

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  • Answers – not organized in an up to date way, and we now have AR LGMD up to 2T.(Yes, I did check to see if they had LGMD2U this morning – better check again shortly.)
  • Examples – only one of the sarcanoglycopathies has a clinical trial available in France; very different counseling for AR LGMD than Becker’s. Ryanodine receptor disorders highest risk for MH, Friedreich’s has DM, scoliosis, cardiomyopathy typically asymptomatic early on and is covered by MDA where other SCAs are not, FSH has risks of Coates-like retinopathy and hearing loss, but not cardiac; EDMD is very high risk for cardiac conduction problems.
  • AFP is for ataxia telangiectasia
  • Make sure what actually gets entered from your orders on these. Julie Kaylor (ACH genetic counselor position) will usually catch them and give you a call. Some flux in when a “good” panel is better than whole exome, may miss some items depending on company and technique, though whole exome is the only way to find genes not previously associated with human disease.
  • Good practice with panel testing – prices not hidden, groupings make sense.
  • These conditions are usually highly distinguishable from each other on a clinical basis. Myotonia with no other features of myotonic dystrophy should not be tested for that, and clinical Becker Thomsen-like cases would not be tested for DM1 or 2.
  • Probably go straight to WES for AMC if a specific diagnosis is needed. Sometimes in a classic sporadic case it may not be as critical.
  • This helps when reading older literature.DES gene can cause AD LGMD1e or myofibrillar disorder,but has just been shown to cause AR LGMD2r as well.
  • Another example is dystrophin, causing Duchenne, Becker, or in some cases cardiomyopathy only.
  • The more newly disocvered genes appear to cause either CMD with CNS anomalies, LGMD with, or LGMD without intellectual disability and may carry a modfier a, b, or c to indicate that.
  • Proteins may not stain normally if they are not in the right places with the proper connections. Glycosylation is apparently critical to correct assembly of the muscle tissue in several locations. Abnormalities of alpha-dystropglycan itself compatible with life are quite rare, and have not been found so far with beta-dystroglycan. The Golgi and ER associated genes in blue are involved in glycosylation and are the 6 identifed first as causing dystroglycanopathies. Reduced staining of dystrophin can be seen with abnormalities of the closely associated proteins, especially the dystroglycan complex as illustrated in the first case presented (2 slides down).
  • ALDA has problems in that answers vary wildly with changing just one item such as presence or absence of CNS structural abnormalities, and this is not necessarily accurate for the newer overlap LGMD/MDDGCs. Very easy to use though and worth registering for. Don’t worry about the YouTube video you cannot access from ACH. They love to hear from users and collect more information on how to try to improve this.
  • These girls had always used KAFOs – I was worried this had caused the remarkable degree of quadriceps weakness, but on getting this diagnosis it was more clearly part of this specific condition.
  • May not be any Rx, could try uridine supplementation, which has been helpful for a few lab mice.
  • TF
  • Neuromuscular Genetic Diagnosis

    1. 1. PROTOCOLS FOR NEUROMUSCULAR GENETIC DIAGNOSIS …the easy problems have been solved already! (mostly)
    2. 2. OBJECTIVES Review the pluses and minuses of the current diagnostic tools  Illuminate some pitfalls we might be able to fall into less often  Shorten and reduce costs of the diagnostic odyssey, while enhancing our likelihood of success and benefit for our patients  Make the case for a true interdisciplinary effort in neuromuscular diagnosis 
    3. 3. WHAT’S WRONG WITH THIS PICTURE? Credit: Jain Foundation, LGMD2I foundation
    4. 4. WHAT DIFFERENCE DOES IT MAKE?  Identify the medical risks       Genetic counseling accuracy     Cardiac Pulmonary Anesthesia/malignant hyperthermia Diabetes, scoliosis, HCM Retinopathy, hearing loss XLR vs AR XLSD vs AD vs mito In some cases, clinical treatments or clinical trials may be available depending on the specific genetic diagnosis Prognosis, what to expect/what helps, support groups
    5. 5. THE TOOLS FOR DIAGNOSIS - $  Family history   Physical exam      Misdiagnosis, misreport, actually getting records Limited by cooperation UMN vs LMN, on a good day Cerebellar versus proprioceptive ataxia Muscle bulk, contracture, facial function, EOM, winging, microcephaly Metabolic (non-genetic lab) tests       Sometimes specific and quick. Sometimes not. CPK, aldolase, TFT AA, OA, isoelectric transferrin, CoQ10, vitamins Lactate/pyruvate – lots of false + and – Alpha-fetoprotein CSF studies
    6. 6. THE TOOLS FOR DIAGNOSIS – $$  Electrodiagnosis         Biopsy      Myopathic vs neuropathic, axonal vs demyelination Kids hate it. Especially repetitive stim, which is not always clear Myotonia is not as specific a finding as you’d like and may not be there in all “myotonic” disorders May be a quick answer for floppy baby (SMA yes or no) UMN lesion can be confounding Very specific for compressive and radicular pathology More likely specific especially on immunostaining or EM Pitfalls with related protein staining affected May be nonspecific myopathic or even normal in some conditions Issues with specimens for send out – research vs clinical Muscle Imaging   Fatty infiltration vs inflammation Affected vs unaffected muscles
    7. 7. THE TOOLS FOR DIAGNOSIS – $$-$$$  Specific single gene tests   PANELS     The good, the bad and the ugly AVOID CMTD, HSP, SCA, DM – not supposed to be “orderable” here Some cover better than WES for specific conditions Microarrays, snp arrays     When common things occur commonly or single best explanation fits pretty well Yield about 15%, towards 20% Now requires consent Regions of homozygosity, duplications, deletions Whole Exome     Requires genetics consultation Expensive and not always covered for parent Best chance for diagnosis of rare condition if Brad Schaefer does not know what it is off the top of his head Tool for discovery of new genes
    8. 8. From Prevention Genetics 3468/PricelistByDisease_11-15-13.pdf
    9. 9. CHARCOT MARIE TOOTH DISEASE(S)  Supect:    Options: Edx or PMP22 dup gene test alone first     Distal weakness, cavus, hypo or areflexia, Commonly +FH, “clumsy” Typical, PN only, no need for other screenings If atypical at all, CMT1x, MPZ, MFN also reasonable to do Edx for slow, very slow, or normal (demyelinating, intermediate, or axonal) Partial panel vs whole exome  DO NOT GET THE FULL PANEL      1a-f = AD, demyelinating 2a-p = AD, axonal 4a-j = AR, demyelinating, internediate or axonal X1-5 (not 3a-e) “ ” Mito and nuclear mito (e.g. PDH), HSANs, SCAs, leukodystrophies also cause hereditary neuropathy
    10. 10. NERVE BIOPSY??  Dejerine-Sottas not genetically specific  PMP22, EGR2 (CMTD 1D, 4E), MPZ, PRX Vasculitic, infectious or other acquired  Sural (sensory) or epidermal for small-fiber  Gene test might be better for amyloid (TTN)   Portugese variant 50% Fabry, Tangier, giant axonal neuropathy  Reference:  
    11. 11. DYSTROPHINOPATHY  Suspects          CPK 4-5 figures, not clinically a myositis Utah dystrophinopathy (or other) gene test Leiden reading frame checker Biopsies?    Global delay in a boy as well as abnormal gait Elevated “LFT” no jaundice, alk phos, GGT OK Floppy baby with contiguous gene syndrome Rhabdmyolysis Research purposes Negative gene test Edx not helpful
    12. 12. MYOTONIA  Suspects for myotonic dystrophy     Myotonia not always present on Edx early   At ACH – get only DM1 for number of repeats NOT PANEL Myotonia Congenita is different disease     Clubfoot, floppy, facial weakness, global delay May be premie and look like or have CP also Adult with cataract, DM, low energy, temporal wasting Becker/Thomsen Strength low for degree of muscle bulk, warm-up CLCN1, SCN4a Also consider     Thyroid disorders Other channelopathies (e.g. KCNJ2/Tawil-Anderson short QT) Brody myopathy (ATP2a1) Some LGMD (especially 1c)
    13. 13. just say no.
    14. 14. ANTERIOR HORN CELL DISEASE     Edx faster, should be confirmed Rough correlation with SMN2 copies and severity Biopsy may also be diagnostic, with group atrophy, not often required Other rare conditions     HBSMA SMARD DSMA - UE AMC
    15. 15. SCA, HSP  Friedreich’s ataxia (frataxin, not fragile X)  Covered by MDA; others are generally not  Cardiomyopathy, diabetes, scoliosis Unless family history positive for specific gene,  Just say WES. (Just my $0.02) 
    16. 16. TRANSITIONS Adhalin = alpha sarcoglycan  SCARMD = sarcoglycanopathy or other LGMD2   High CPK with some dystrophin on biopsy ≠ Becker’s In 2006 had six genes for dystroglycanopathy, 50% undiagnosed, now about 15 and fewer  Some conditions caused by more than one gene  Some genes cause more than one condition  Conditions vary with what is wrong with the gene  Some genes can cause disease as AR or AD  Conditions vary depending on other genes  What will we do when we run out of letters?   Only 6 more LGMDs to go…
    17. 17. CLASSIFICATIONS OF MUSCLE DISEASE   Congenital Myopathy Congenital Muscular Dystrophy         Dystrophinopathy EDMD FSHMD Limb Girdle   Collagen Related (Bethlem/Ullrich) Dystroglycanopathy Merosin-deficient and related Rigid spine SEPN, Integrins, etc. Dominant, recessive, distal Myasthenia and myasthenic syndromes
    18. 18. EXAMPLE: LMNA Nuclear envelope gene, aka Lamin A/C  Emery-Dreifuss muscular dystrophy  Scapuloperoneal, cardiac conduction concerns  EDMD 2 and 3, AD  (vs. SYNE1, SYNE2, FHL or x-linked with emerin)  LGMD1B AD “laminopathy”  CMT2B1 AR   p.R644C missense mutation in the lamin A/C protein Familial partial lipodystrophy FPLD2 AD  Dilated cardiomyopathy CMD1A  Hutchinson-Gilford progeria   Due to farnesylated mutant prelamin A (progerin)
    19. 19. EXAMPLE: GLYCOSYLATION BUILDING CROSSWALKS      LGMD2I = MDDGC5 = MDC1C (FKRP) LGMD2K = MDDGC1 (POMT1) LGMD2N = MDDGC2 (POMT2) LGMD2O = MDDGC3 (POMGNT1) LGMD2M = MDDGC4 (FKTN)     LGMD2P = MDDGC9 (DAG1) LGMD2T = MDDGC14 (GMPPB) with/without ID, seizures      Japanese severe form of CMD Compare with MDC1a, merosin aka alpha-laminin We have one case – U of Iowa fibroblast culture rescue technique Walker-Warburg can be several of the above Santavuori (MEB) “cobblestone” usually POMgnT1 “Partial merosin-deficient” likely in this group (MDC1B,D,E or new) CDGS    Classic with transferrin isoelectric focusing Overlap with dystroclycanopathy (DPMs) Brand new (PIGT) – we have two siblings, diagnosed by WES at NIH
    21. 21. LGMD & THE JAIN FOUNDATION TOOL   Primarily for LGMD2B, dysferlinopathy Concept is to determine probability and concordance based on clinical evaluation, FH, CPK, optionally biopsy and brain MRI    They got 45/50 if first position, 3/7 if 2 or 3 A route to free 2B or 2I testing Otherwise, great concept but does not quite work yet…     We got 1/12 specific (low concordance on a 2B) We got 4/12 dystroglycanopathy non-specific “definitively excluding conditions based on the presence or absence of any one symptom isn't a good approach” Working on it, adding Pompe, DYS carrier, etc.   Automated LGMD Diagnostic Assistant (ALDA)
    22. 22. TWO “EASY” CASES  Young girl, brought in as affected DMD female due to biopsy with abnormal dystrophin after high CPK noted    Dystrophin gene normal Phenotype merosin-deficient, confirmed genetically Young man, looked like DMD     Dystrophin gene normal, CPK 8,000 Immunostaining with reduced c-terminal dystrophin, COL6, alpha-dystroglycan, abnormal dysferlin and caveolin pattern Clinically not Bethlem-Ullrich, CNS near normal Selected LGMD2 gene tests, 2I was positive
    23. 23. TWO “OTHER” CASES Two girls, one more severely affected  Cataracts, club foot, intellectual disability  Carrying diagnosis of AMC  Genetics conference – consider DM1 vs WES  Whole exome indicates CMT 2O (dynamin)  Dynein defect reports more similar phenotype but the two form a complex  Mom is low level mosaic  Edx (and publication?) pending… 
    24. 24. THIS WENT RIGHT TO WES, RIGHTLY Very severe Duchenne-like presentation  4 year old boy, weak from about 1 year of age, progressing rapidly  CPK only 264, lactate/pyruvate 21./1.6  Biopsy “mixed myopathic” normal immunostaining  WES had defect in thymidine kinase (TK2)  Autosomal recessive  Might also have been found in ROH on snp array  Mitochondrial DNA depletion, myopathic form 
    25. 25. CONCLUSIONS        Single gene test if they walk in out of the textbook, or known diagnosis in family Non-genetic tests where helpful to narrow it down Only a few of the panel tests make sense – ask Julie! – could it really be ANY of the genes included? SNP array, mito sequencing may be first step especially if consanguinity or dysmorphism WES if many possible categories, many possible genes, panels more expensive NIH seems better than Mayo if we are still stuck (Mayo does not take AR Medicaid) Genetics, genetic counselors, neuro, pathology, rehab can all offer clues to differential diagnosis and management – what would happen if we put our heads together?
    26. 26. POST TEST (Easy – T/F) Neuromuscular diagnosis should usually include a CPK  Neuromuscular diagnosis should always include electrodiagnosis and biopsy 