Linkage mapping of the gene for Charcot-Marie-Tooth disease type 2 to chromosome 1p (CMT2A) and the clinical features of CMT2A.

Charcot-Marie-Tooth disease type 2 (CMT2) is characterized by a motor conduction velocity of the median nerve of > 38 m/sec and is a genetically heterogeneous disorder with at least three loci identified: CMT2A (1p35-36), CMT2B (3q13-22), CMT2C (not linked to any known loci), and CMT2D (7p14). In this study, we performed linkage analysis of two Japanese CMT2 families using markers flanking the CMT2A, CMT2B, and CMT2D loci. The highest cumulative multipoint lod score of 3.69 was obtained at D1S244. The CMT2B and CMT2D loci were excluded by the results of linkage analysis performed using markers D3S1551, D3S1290, and D7S484. The clinical features of the CMT2A affecting the two families include similar levels of muscle weakness of the posterior and anterior tibial muscles, tendon reflexes preserved in upper extremities but reduced or absent in lower extremities, no enlargement of the peripheral nerves, and mild sensory disturbance in only 20% of affected individuals.