Nemaline myopathy: histological, histochemical and ultrastructural studies.

Histological, histochemical and ultrastructural studies were performed on muscle biopsies from three siblings with congenital nemaline myopathy. Histological studies revealed type I fibre atrophy and type II fibre paucity. Ultrastructural studies of intramuscular nerves showed that the axonal diameters were very narrow compared with the width of myelin lamellae. Granular or membranous osmiophilic material occurred in the adaxonal Schwann cell cytoplasm and had a periodicity of 33--38 A. The neuromuscular junctions showed degenerative features such as glycogen granules or myelin figures in 27.1% of total terminal axons. The secondary synaptic clefts were markedly decreased in number and short in length. Myotendinous junction-like structures were found in 5.5% of the muscle fibres near the neuromuscular junctions, and often near sites of fibre-splitting. Rods in nemaline myopathy might be caused as a result of longitudinal splitting and disruption of fibres due to deficient regeneration of the muscle fibres associated with neurotrophic abnormalities.