inherited myopathies

1. INHERITED MYOPATHIES

2. Muscular
Dystrophy
Metabolic
Myopathy
Mitochondrial
Myopathy
Congenital
Myopathy

3. MUSCULAR DYSTROPHY

4. Muscle dystrophies include several inherited disorders of skeletal muscle.
Common features:
03
01
02
Childhood or Young adulthood
Manifestation:
Progressive muscular weakness
Cardinal Symptom:
Myonecrosis, Regeneration & Fibrosis
Histopathologic Criteria:

5. • Most of the muscular dystrophies are
due to break down of the dystrophin-
glycoprotein complex.
Network of fibrous proteins - that binds myofibers
to the extra cellular matrix – mechanically stabilizes
sarcolemma during contraction & relaxation
Loss of integrity of DGC causes stress fractures of
sarcolemma during muscle contraction.
Influx of CALCIUM through theses breaks
Activates proteolytic enzymes leading to
autodigestion of sarcoplasm (MYONECROSIS).

6. DYSTROPHIN
( Intracellular )
SARCOGLYCANS
&
β DYSTROGLYCAN
( Transmembrane proteins )
Anchors ACTIN to sarcolemma
& other DGC proteins
Interacts with ECM
DYSTROPHIN GLYCOPROTEIN COMPLEX
α-DYSTROGLYCAN
( Extracellular)
Other Cytoplasmic Proteins:
Dystrobrevin
Syntrophins
Neuronal nitric oxide synthase.

7. DYSTROPHIN
( Intracellular )
SARCOGLYCANS
&
DYSTROGLYCANS
( Transmembrane proteins )
Anchors ACTIN to sarcolemma
& other DGC proteins
Interacts with ECM
Duchenne MD
Becker MD
Limb Girdle MD
Congenital MD

8. TYPES
of Muscular
Dystrophies
 X linked
o Duchenne Muscular Dystrophy
o Becker’s Muscular Dystrophy
o Emery-Dreifuss Muscular Dystrophy
 Autosomal Dominant
o Fascioscapulohumeral Muscular Dystrophy
o Myotonic Dystrophy (DM1 & DM2)
o Limb-Girdle Muscular Dystrophies (LGMD 1)
o Occulopharyngeal Muscular Dystrophy
 Autosomal Recessive
o Limb-Girdle Muscular Dystrophy (LGMD 2)
o Congenital Muscular Dystrophy
Children – DMD
Adults – DM & LGMD

9. X – LINKED MD

10. DUCHENNE MUSCULAR DYSTROPHY
• Commonest.
• INCIDENCE : 1 per 3500 live male births
• Severely progressive phenotype.

11. • PATHOGENESIS:
Deletion or Frame Shift
mutations in DYSTROPHIN gene
Loss-of-function mutations
in dystrophin gene.
Total absence of
Dystrophin protein
DMD
DYSTROPHIN GENE:
• On X chromosome at Xp21.
• One of the largest human genes.
• 2.3 million bp & 79 exons
• Encodes for DYSTROPHIN PROTEIN.

12. Results in
myofiber
degeneration.

13. CLINICAL FEATURES:
• Boys with DMD are normal at birth.
• Very early motor milestones are met on time.
• Walking is often delayed.
• 1st indications of muscle weakness - clumsiness and inability to keep
up with peers.
• Weakness begins in the pelvic girdle muscles and then extends to the
shoulder girdle.
• Enlargement of the muscles of the lower leg associated with
weakness, a phenomenon - pseudohypertrophy.
• Initially by an increase in the size of the muscle fibres and then, as the muscle
atrophies, by an increase in fat and connective tissue.
• Dystrophin is also expressed in heart & CNS.
• Heart – cardiomyopathy & arrhythmias.
• CNS – cognitive impairment & frank mental retardation.
DEATH – at 25 to 30 yrs - respiratory insufficiency, pulmonary infection
or heart failure.

14. History + Physical Examination + Laboratory Studies.
S. Creatine Kinase – markedly raised during first
decade of life (due to ongoing muscle damage)
Level falls as disease progresses.
Muscle biopsy – myonecrosis, phagocytosis,
regeneration & non specific structural changes (eg,
central nuclei, split fibres, atrophic & deformed fibers).
Increased endomysial connective tissue & fat.
Dystrophin Stain – negative
Genetic studies – presence of Dystrophin mutation.
DIAGNOSIS

15. EARLY DMD
 Sizes: Varied
Myopathic groups :
 Clusters of small necrotic
(Black arrow) &
 regenerating (White arrow)
muscle fibers
 Internal nuclei: Occasional
 Endomysial connective
tissue: Normal to mildly
increased

16. DMD SEVERE
 Endomysial
connective tissue:
Increased
 Muscle fibers
Necrosis &
Regeneration
Size: Varied

17. DMD: Later pathology
 Fiber size: Varied
 Endomysial connective
tissue: Increased
 Fat replacement of muscle:
Prominent

18. Dystrophin Stain
Normal DMD

19. BECKER MUSCULAR DYSTROPHY
FEATURES DMD BMD
Cause Mutation of Dystrophin Gene (called DYSTROPHINOPATHIES)
Type of Mutation Frame Shift Inframe deletion or Duplication or
Missence mutation
Dystrophin Protein Absent Reduced + Abnormal structure
Onset Early Late
Form Severe Milder
Rate of Progression Faster Slower
Histopathology Severe changes Less severe
Dystrophin Stain Negative Positive BUT ABNORMAL STAINING
PATTERN

20. ANTIDYSTROPHIN
ANTIBODIES are used
since amount of
dystrophin in BMD
may be synthesised in
sufficient quantities to
give a positive
immunostain.
a, c & e - Controls
DYS1 – epitopes in rod
domain: Absent
DYS2 – near C-terminus:
Positive but Reduced
DYS3 – near N-
terminus:
Positive but Reduced

21. EMERY-DREIFUSS MUSCULAR DYSTROPHY
• Caused by mutations in genes that encode for nuclear lamina protein.
• The diagnostic triad includes
 Slowly progressive humeroperoneal myopathy,
 early contractures of major tendons (eg Achilles, spine, elbow)
 cardiomyopathy with associated conduction defect.
• Symptoms usually appear during the first decade of life.
EMD 1 EMD 2
X - Linked Autosomal
Mutations in EMD gene – Xq28 Mutations in LMNA gene – 1q22
Encodes for emerin Encodes for Lamin A and C
Both are localized to inner face of nuclear membrane
Maintain shape & mechanical stability of nuclear membrane during muscular contraction

22. • Serum CK levels - may be elevated (lower than dystrophinopathies).
• Skeletal muscle biopsy - evidence of dystrophy.
• Electron microscopy - alterations in nuclear architecture .
• Gene sequencing - gold standard.

23. AUTOSOMAL DOMINANT

24. MYOTONIC DYSTROPHY
• “MYOTONICA DYSTROPHICA”
• Multisystem disorder associated with skeletal muscle weakness, cataracts, endocrinopathy
& cardiomyopathy.
• Key feature – MYOTONIA – sustained involuntary contraction of muscles.
• INCIDENCE : 1 in 10,000.

25. CLINICAL FEATURES:
• Slow progressive weakness of face,
jaw and distal limb
• Frontal baldness, ptosis, and atrophy
in the temporalis and masseter
muscles result in a characteristic
“hatchet-faced” appearance.
• Dysarthria and dysphagia
• Myotonia
GIT
• Low motility
• Constipation
• Pseudo-
obstruction
HEART
• Cardiomyopat
hy
• Conduction
defects
LUNGS
• Hyypoventilla
tion
• Sleep apnea
• Aspiration
pneumonia
BRAIN
• Behaviour &
cognitive
abnormalities
ENDOCRINE
• Testicular
atrophy
• Hypothyroidis
m
• Diabetes
EYE
• Cataract
• Ptosis
SKIN
• Premature
balding

26. TYPES DM 1 DM 2
Other name Steinert Disease Ricker Syndrome
Gene affected DMPK ZNF9
TNR CTG CCTG
Number of repeats (normal 5 to 34) > 100 > 75 – 11,000
Forms Congenital, juvenile & adults After 3rd decade
Predominant weakness Distal Proximal

28. H&E
Internalisation of nuclei
Pyknotic nuclear clumps
NADH stain
Type I (darker) fibers: Smaller (selective
atrophy of type 1 fibers)
Internal architecture: Disordered
Ring fibres
Diagnosis is made on the combination of these findings

29. FASCIOSCAPULOHUMERAL DYSTROPHY
• Has a characteristic pattern of
muscle involvement: voluntary
musculature of face, shoulder girdle
& upper extremities.
• INCIDENCE : 1 in 20,000.

30. Patients with FSHD inherit an abnormally small number of
SUBTELOMERIC REPEATS on long arm of chromosome 4
Each repeat carries a copy of DUX4 gene
Deletion of these flanking repeats – causes a change in chromatin
“depresses” the remaining copies of DUX4 gene
“Overexpression” of DUX4

31. DUX4 is expressed at high levels
Single Nucleotide
Polymorphisms
Repeat contractions
Pathogenic
FSHD
SNPs at positions
immediately 3’ of
the DUX coding
sequence

32. H&E stain
Muscle fibers
 Size: Varied;
Atrophy & Hypertrophy
 Pathology: Necrosis,
Regeneration &
Inflammation
 Diagnosis is made
by Molecular
Genetic testing of
D4Z4 repeats at
4q35 (DUX4
encoded within
these repeats)

33. OCCULOPHARYNGEAL MUSCULAR DYSTROPHY
• Late onset mild myopathy – begins in middle life.
• CF: ptosis, ophthalmoplegia & dysphagia.
• Short GCG expansion (8-13) in the poly(A)-binding protein gene on chromosome 14
Results in abnormal accumulation of protein PABP2
Forms INCLUSIONS in the nucleus

34. H&E
Mild dystrophic changes, nuclear internalisation,
fiber atrophy & interstitial fibrosis
Occasionally vacuoles may be seen

35. Electron Microscopy
Nuclear inclusion – unbranched tubulofilamentous
structures

36. LIMB-GIRDLE MUSCULAR DYSTROPHY
• Heterogenous group of 6 AD (LGMD1) & 15 AR (LGMD2) entities
– with a common feature of proximal axial muscle involvement.
• INCIDENCE : 1 in 25,000 to 50,000
• Age of onset & disease severity are highly variable.

37. LGMD 1 GENE PROTEIN
1A MYOT Myotilin
1B LMNA Lamin A/C
1C CAV3 Caveolin 3
1D DNAJB6 HSP40
1E DES Desmin
1F TNPO3 Transportin 3

38. AUTOSOMAL RECESSIVE

39. LIMB-GIRDLE MUSCULAR DYSTROPHY
• LGMD 2 – 15 entities

40. LGMD 2 GENE PROTEIN
2A CAPN3 Calpain-3
2B DYSF Dysferlin
2C SCGC Gamma- sarcoglycan
2D SCGA α- sarcoglycan
2E SCGB β- sarcoglycan
2F SCGD δ- sarcoglycan
2G TCAP Telethonin
2H TRIM32 Tripartite motif containing 32
2I FKRP Fukutin-related protein
2J TTN Titin
2K POMT1 Protein-O-mannosyltransferase1
2L ANO5 Anoctamin 5
2M FKTN Fukutin
2N POMT2 Protein-O-mannosyltransferase2
2O POMGnT1 O-linked mannose beta 1,2-N- acylglucosaminyltransferase
2Q PLEC1 Plectin 1

41. Myopathic changes of
varying severity can be seen
– eg,
• Myonecrosis
• NS structural changes split
fibers, internal nucleus,
atrophy, endomysial
fibrosis
DIAGNOSIS is made on IHC
using specific antibodies
against deficient proteins.

42. CONGENITAL MUSCULAR DYSTROPHY
• Present at birth or soon after.
• CF : hypotonia, weakness & developmental delay.
• Nonprogressive & static muscle disease
• CK – elevated or normal
• Biopsy – NS findings:
o Initially – myofiber atrophy
o Later – myofiber loss & fat replacement
Similar to Congenital Myopathies

43. CMD TYPES Deficiency
MEROSIN-deficient Merosin (α-Laminin) White matter abnormality
ULRICH Collagen VI
Abnormal Glycosylation of
α-dystroglycan
α-dystroglycan Includes
Fukuyama CMD – Japan
Muscle-Eye-Brain Disease
Walker-Warburg Syndrome

44. Normal Merosin - negative
MEROSIN

45. COLLAGEN VI
Normal Abnormal granular deposition

46. Muscle fiber size: Varied
Basophilic fibers: Scattered
Endomysial connective tissue: Increased
H & E Gomori Trichrome stain NADH stain
FUKUYAMA CMD
Scattered small immature
muscle fibers with
coarse internal architecture

47. CONGENITAL MYOPATHY

48. • Characterised by structural abnormalities of myofibers.
• Wide clinical range.
• Static or slowly progressive course
• CF : proximal & facial weakness, dysmorphic features, kyphoscoliosis etc.
• Severe cases – manifest before birth – decreased fetal movements & polyhydramnios.
• Cause severe hypotonia & weakness at birth, respiratory failure & inability to
swallow – “floppy infant”.
• ~12% die in first year of life.
• CK – Normal.
• DIAGNOSIS : muscle biopsy & genetic testing.

49. • Nomenclature is based on the pathologic changes.
CENTRAL CORE
DISEASE
NEMALINE
MYOPATHY
CENTRONUCLEAR
MYOPATHY
CONGENITAL
FIBER TYPE
DISPROPORTION

50. CENTRAL-CORE DISEASE
• AD / AR
• Mutations in RYR1 gene ( Ryanodine Receptor 1)
Encodes for Calcium channels in Sarcoplasmic Reticulum.
• CCD myofibers have a central area (core) with disrupted arrangement of sarcomeres and
decrease in mitochondria number.
• Some may develop malignant hyperthermia.

51. NADH stain
• Central clear zone in fibers stained for cytoplasmic or
mitochondrial membranes
• NADH stain: Well defined central region of reduced staining
• Cores run whole length of muscle fibers
 Predominance of type 1 fibers.
H & E - Central cores not evident

52. NADH Stain
Multicore

53. NEMALINE MYOPATHY
• Aka “Rod” Myopathy – aggregates of spindle shaped particles.
• AD or AR.
NEM type INHERITENCE GENE PROTEIN
1 AD TPM3 a-tropomyosin 3
2 AR NEB Nebulin
3 AR ACTA a-actin 1
4 AR TPM2 Tropomyosin 2
5 AR TNNT1 Troponin T1
7 AR CFL2 Coffilin 2

54. The rod shaped structures are composed of a-actinin – the main protein of Z- bands – best seen on Gomori Trichrome
stain, Toluidine blue stain & Electron Microscopy.
GT Stain
EM
TB Stain

55. CENTRONUCLEAR MYOPATHY
• Central areas of myofibers – nucleus without contractile filaments ~immature fetal muscle.
• Aka “Myotubular” Myopathy.
TYPE GENE PROTEIN
X-Linked (most severe) MTM1 Myotubularin
AD DNM2 Dynamin-2
AR BIN1 Amphiphysin-2

56. H & E
Nucleus:
• Central
• Increased in size
• Vesicular chromatin

57. CONGENITAL FIBER TYPE DISPROPORTION
• Predominance & Atrophy of type 1 fibres.
• Mutations :
GENE PROTEIN ASSOCIATED WITH
SEPN1 Selenoprotein 1 Protein Aggregate Myopathy & Rigid Spine MD
ACTA 1 α-actin 1 Protein Aggregate Myopathy & Nemaline
Myopathy
TPM3 Tropomyosin 3 Nemaline Myopathy

58. METABOLIC MYOPATHY
(DISORDERS OF GLYCOGEN OR LIPID METABOLISM)

59. DISORDERS OF GLYCOGEN METABOLISM
McArdle Disease
• Myophosphorylase deficiency (Glycogenosis type V)
• CF: Episodic muscle damage with exercise – pts are unable to break down α-1,4-glucoside
linkages.
• Biopsy – crescentic, empty vacuoles in subsarcolemmal location.

60. POMPE DISEASE
• Acid Maltase deficiency ( Glycogenosis type II).
• Impaired lysosomal conversion of glycogen to glucose – glycogen accumulate within
lysosomes.
• Severe deficiency – generalised glyosgenosis.
• Milder – progressive adult onset, involve respiratory & truncal muscles – better prognosis.
• Biopsy – Glycogen filled vacuoles in sarcoplasm.

61. McArdle Disease
crescentic, empty vacuoles in subsarcolemmal location
H & E H & E
Pompe Disease
Glycogen filled vacuoles in sarcoplasm

62. DISEASES OF LIPID METABOLISM
• Seen in :
o Primary Carnitine Deficiency,
o Carnitine Palmitoyltransferase deficiency (CPD) – most common
o Neutral Lipid Storage Disease
o Multiple acetyl-coenzyme A Dehydrogenase Deficiency.
• In CPD – deficiency of Carnitine - Impaired transport of free fatty acids into mitochondria.
• CF : Proximal Muscle weakness & Cardiomyopathy.

63.  Small, clear vacuoles: H & E, GT
 Abnormal internal architecture with a punctate pattern: NADH & SDH
 Large lipid droplets in type I muscle fibers: Sudan black
H & E NADHGomori Trichrome
Sudan Black

64. ELECTRON MICROSCOPY
Top fiber: Lipid is Abundant
Bottom fiber: Minor increased lipid

65. MITOCHONDRIAL MYOPATHIES

66. • Mitochondrial Diseases are complex systemic conditions that can involve many organ
systems, including skeletal muscle.
• Variable involvement of muscle weakness – Extraocular Eye muscles is common.
• Mutations – impair the ability of mitochondria to generate ATP.
Tend to affect tissues with high ATP requirements.
Skeletal Muscles, Cardiac Muscle & Neurons
• Mitochondrial Proteins – encoded by
Highest
mitochondria
per mass
Nuclear genome
Mitochondrial genome
Mitochondrial Diseases develop
only when a certain threshold of
mutated mtDNA copies exceed
within a substantial fraction of
“at-risk” cells.

67. Ragged Red Muscle Fibers
Myofibers with mitochondrial
proliferation: Clear, or stained,
external rim
Cytochrome oxidase (COX) – Negative
• COX staining is markedly reduced
• Punctate mitochondria are reduced
or not visible
H & E stain Gomori Trichrome stain

68. ELECTRON MICROGRAPS:
• Morphologically abnormal mitochondria-
• accumulated in subsarcolemmal region
• with concentric membranous rings
(“phonographic records”) and
• rhomboid paracrystalline inclusion
Longitudinal section

69. SPINAL MUSCULAR ATROPHY

70. • SMA is a neuropathic disorder in which loss of motor neurons leads to muscle
weakness & atrophy.
• AR
• INCIDENCE : 1 in 6,000 births.
• Loss-of-function mutation in SMN1 gene (Survival of Motor Neuron 1)
Loss of motor neurons in utero
Results in denervation of skeletal muscles

71. SMA TYPES FEATURES
I – a & b (severe) <6 months
Classic “floppy baby”
II (intermediate) 6-8 months
Delayed motor milestones
Scoliosis, joint contracture,
intercostal muscle weakness.
III – a & b (mild)  18 months
 Hand tremor, scoliosis, hip
abductus weakness
IV (adult) 2nd to 3rd decade of life
Mild motor weakness
V Distal SMA

72. MUSCLE BIOPSY APPROACH

73. ABNORMAL
MYOFIBRES
Size
Shape
Glycogen / Lipid / Mitochondrial
Internal
Architecture
Storage / Accumulated Material
Small
Large
Rounded Angular
Myopathic Neurogenic
Disordered – DM
Internal Nuclei – DM, LGMD, OPMD
Inclusion - OPMD
Distribution
Scattered – Acute neuropathic or Myopathic changes
Uniform - Dystrophy
Regional
Myopathic – Grouping – DMD
Varied – FSHD, CMD
Neurogenic – progressive de & reinnervation

74. THANK YOU