These are the non-dystrophic congenital myopathies
Nemaline myopathy a.k.a. nemaline rod myopathy:
Floppy infant with facial weakness and respiratory insufficiency.
Also see adult from a.k.a. sporadic late onset nemaline myopathy
Autosomal dominant, autosomal recessive
Mutations in the following Proteins:
- Alpha-skeletal actin
HE fibre atrophy without grouping, subsarcolemmal increased eosinophilic staining. GMT subsarcolemmal purple/red nemaline rods in type 1 fibres. Often type 1 fibre hypertrophy, type 1 fibre predominance.
EM: nemaline rods= osmiophilic rods
Immunohistochemistry: Alpha actinin type 2 positive rods in a lot of cases,
Note: nemaline rods can occur in inflammatory muscle disease and in central core disease.
Also see adult from a.k.a. sporadic late onset nemaline myopathy.
Centronuclear myopathy a.k.a. myotubular myopathy:
A group of genetic disorders: infantile (X linked), childhood (autosomal dominant, autosomal recessive), adult (autosomal dominant)
Type 1 fibres: Central nuclei and small. Normal type 2 fibres usually.
Type 1 fibre predominance.
Central core disease:
Floppy infant: hypotonia
Childhood and adults. Proximal weakness, neck flexors and facial muscles. Associated with skeletal abnormalities scoliosis, developmental dysplasia of the hip
A group of disorders:
- Autosomal dominant,
- Rarely recessive (multiminicore disease)
- RYR1 gene ryanodine receptor mutation (Ca++ channel).
Type 1 fibres: central area devoid of staining with NADH, also devoid of staining with SDH and COX
Strong Type 1 fibre predominance.
Myopathic features may occur
EM: central areas devoid of mitochondria extending the full length of the muscle fibre