HEREDITARY MOTOR AND SENSORY NEUROPATHY IIB - CLINICAL AND ELECTRODIAGNOSTIC CHARACTERISTICS

Axonal forms of autosomal dominant hereditary motor and sensory neurop athies (HMSNs) represent a heterogeneous group of disorders based on g enetic linkage studies. We recently identified one large family with a xonal HMSN exhibiting linkage to chromosome 3q, designated HMSN IIB, a nd report here the clinical and electrodiagnostic features. We clinica lly evaluated 10 individuals with HMSN IIB and performed detailed elec trophysiologic studies in 5 of these patients. HMSN IIB is characteriz ed clinically by the presence of distal symmetric motor weakness and p rominent sensory loss affecting the lower extremities with preserved a nkle reflexes. Symptomatic age at onset is in the second or early thir d decade of life. Six patients with HMSN IIB had distal trophic ulcera tions in the feet, leading to eventual toe amputations in four cases. Electrodiagnostic studies confirmed a distal sensorimotor axonopathy i nvolving the lower limbs with normal motor conduction velocities. Tibi al II-reflexes were preserved in HMSN IIB, despite the uniform loss of sural nerve potentials. Overall, individuals with HMSN IIB demonstrat ed a consistent clinical and electrodiagnostic phenotype that had no o verlap with genetically unaffected family members. The identification of specific clinical and electrodiagnostic features of HMSN IIB may pr ove useful in the diagnosis and differentiation between various subtyp es of HMSN II.