[Clinical phenotype of Charcot-Marie-Tooth disease (CMT) and familial amyloid polyneuropathy (FAP)]

Abstract

A nationwide study of CMT and FAP has been performed. In FAP TTR Met30 families with late onset, neuropathy showed male preponderance, low penetrance, little relationship to endemic foci, sensorimotor symptoms beginning distally in the lower extremities with disturbance of both superficial and deep sensation, and relatively mild autonomic symptoms, consistent with pathological findings. In contrast, families with early onset showed higher penetrance, concentration in endemic foci, predominant loss of superficial sensation, severe autonomic dysfunction. Demyelinating versus axonal phenotypes are major issues in CMT. CMT1A duplication caused mainly demyelinating phenotype, while axonal features were variably present. In CMT1B, two distinctive phenotypic subgroups were present: one showed exclusively axonal features; and another was exclusively demyelinating. CMTX showed intermediate slowing of MCV, predominantly axonal features, and relatively mild demyelinating pathology. Differing from CMT1B, these axonal and demyelinating features were concomitantly present in individual patients in variable extent. Median nerve MCVs were well maintained independently of age, disease duration, and severity of clinical and pathologic abnormalities. Amplitude of CMAPs was correlated significantly with distal muscle strength, indicating that clinical weakness results from reduced numbers of functional large axons, not from demyelination. CMT patients with demyelinating and/or axonal features, together with FAP patients with axonal feature and scattered distribution, are supposed to increase according to the development of genetic diagnosis for hereditary neuropathy that verifies late-onset, de novo and asymptomatic patients.