Asymmetric Phenotype Associated With Rare Myelin Protein Zero Mutation

Abstract

Myelin protein zero (MPZ) mutations cause demyelinating neuropathies that range from severe neonatal to milder adult forms. We report a 36-year-old man who developed weakness of his left little finger adduction 3 years earlier. The weakness progressed to his other limbs. Examination revealed mildly high-arched feet with asymmetric weakness of ulnar-innervated muscles (left > right) and asymmetric weakness of peroneal-innervated muscles (right > left). Motor nerve conduction velocities ranged from 18.4 to 24.4 m/s in the upper extremities and from 14.8 to 22.7 in the lower extremities. Left median partial motor conduction block was noted at the forearm segment. Genetic testing demonstrated MPZ mutation with ARG98HIS amino acid change. The patient's father is a 68-year-old man who was asymptomatic and who was noticed to have high-arched feet and asymmetric leg muscle atrophy and weakness (right > left). The patient's 2-year-old son is "clumsy" with history of neonatal laryngomalacia. He has flat feet, areflexia, and difficulty standing on individual right versus left leg. The patient's paternal grandfather had high-arched feet and hearing loss. We conclude that ARG98HIS MPZ mutation may cause hereditary and relatively mild and asymmetric demyelinating sensorimotor polyneuropathy.