Hereditary motor and sensory neuropathy with optic atrophy. Ultrastructural and morphometric observations on nerve fibers, mitochondria, and dense-cored vesicles.

Nerve biopsy specimens from three cases of hereditary motor and sensory neuropathy with optic atrophy were studied by light and electron microscopy and by morphometry. All cases had a chronic neuropathy of the neuronal/axonal type with little, presumably secondary, demyelination. There was predominant reduction of the large-caliber population of myelinated and unmyelinated nerve fibers. The number of dense-cored vesicles in unmyelinated and small myelinated fibers was increased. Abnormal mitochondria in Schwann cells with paracrystalline inclusions, prominent cristae including paracrystalline material (cases 1 and 2), and axonal mitochondria with presumable hydroxyapatite crystals (case 3) were found. The morphologic results suggest that hereditary motor and sensory neuropathy with optic atrophy should be regarded as a separate entity within the hereditary motor and sensory neuropathy group.