Histopathological Findings in Hereditary Motor and Sensory Neuropathy of Axonal Type with Onset in Early Childhood Associated with Mitofusin 2 Mutations

Neuropathologic abnormalities can be sufficiently characteristic to suggest the genetic basis of some hereditary neuropathies such as those associated with mutations in MPZ, GJB1, GDAP1, MTMR2, SH3TC2, PRX, FGD4, and LMNA. We analyzed the morphologic features of 9 sural nerve biopsies from 6 patients with mutations of mitofusin 2. All patients presented in early childhood with axonal neuropathies designated as mild or severe motor and sensory neuropathy. In all cases, there was a marked decrease in density of myelinated fibers, mainly of large diameter fibers. These changes were more marked in the second biopsies of 3 patients that were performed from 7 to 19 years after the first biopsies. Neurophysiologic findings were most suggestive of axonal degeneration, but some onion bulbs were present in all cases. Axonal mitochondria were smaller than normal, were round, and were abnormally aggregated. These changes may result from abnormal mitochondrial fusion and fission. The results suggest that these clinical and pathological features may be sufficiently characteristic to suggest the diagnosis of mitofusin 2-related neuropathy.