[Correlation of heredity and environmental factors in the etiology of Vilyui encephalomyelitis. I. Patient frequency in families].

Viljuisk encephalomyelitis (VE) is a severe neurologic disease characterized by slow progressive dementia', oligobradykinesia, low spastic paraparesis and speech disturbances. It develops in persons of 20-50 years old. VE occurs in a small region of middle Viljui, but for last years the focus has considerably expanded. Etiology of VE is still obscure. 194 families with VE patients were examined. The data obtained contradict the hypothesis of simple recessive inheritance of VE. The value of the heredity coefficient, calculated on the basis of the Falconer - Edwards model, is 22-29% for relatives of the first relation degree. It suggests the existence of individual hereditary determined susceptibility to VE. 14 secondary cases were observed in affected families among adopted relatives (adopted children, husbands and wives of patients) with a rate exceeding random possible frequency. These observations have been evaluated as an evidence of horizontal transmission of the disease from patients with chronic forms to healthy persons. Obligatory condition for the transmission consists in a long-term contact (as a rule, more than one year). According to all known characteristics VE should be refferred to slow infections.