Hereditary motor-sensory neuropathy 1X (НМСН 1X) is the second frequent form of hereditary motor-sensory neuropathies caused by mutations in the GJB1 gene (gap junction B1 type). The authors have established earlier that the с.259C>G (р.P87A) mutation is the most frequent cause of НМСН 1Х (92%) in patients from the Republic of Bashkortostan.To study in details the territorial ethnic distribution and clinical manifestations of the с.259C>G (р.P87A) in the GJB1 gene in patients with НМСН 1Х from the Republic of Bashkortostan.Clinical/neurological data were assessed in 52 patients (32 men and 20 women) from 13 families with this НМСН 1Х mutation in accordance to the diagnostic criteria of the European neuromuscular center. Twenty-three patients underwent standard electroneuromyographic study ('Nicolet Viking quest') using cutaneous electrodes. Data analysis was performed with Statistica ver.6.0 ('Stat Soft, Inc.', 2003) software.The с.259C>G (р.P87A) mutation was more frequent in Bashkir (61%) and Russian (31%) families from 6 areas of the Republic of Bashkortostan. The age-at-onset was 13.24±4.33 years in men. In women, the age-at-onset varied from 7 to 45 years, it was difficult to detect this parameter in several patients due to the absence of complaints and symptoms of disease. A comparative analysis revealed the higher degree of peripheral nerve lesions in men compared to women. There was the distinct difference in electrophysiological parameters (excitation spreading velocity and M-response amplitude) along motor fibers of the middle nerves between men and women that indicated the predominantly demyelinating character of the pathological process in men and the axonal character in women.Clear clinical/electrophysiological sex differences (intra- and inter family) were shown in patients with НМСН IX with the с.259C>G (р.P87A) mutation in the GJB1 gene. The disease was less severe and often with the absence of symptoms in women. Genetic testing for mutations in the GJB1 gene, including the с.259C>G (р.P87A) mutation, can be recommended to female patients with excitation spreading velocity >38m/s.