[Hereditary conduction defect in the His system: a dominant autosome disease].

An oriental family with over 265 living descendants of a polygamous ancestor known to have had a slow pulse and syncopes was studied. Many examples of conduction defects, mainly right bundle branch block, left anterior hemiblock, bifascicular block and artioventricular block were detected. The transmission of the genetic defect was autosomal dominant, the incidence 43%, the penetration very variable, apparently affecting the male descendants predominantly, the expression probably congenital, but with complete heart block presenting at 75 years of age in one case. The localisation of the conduction defect is discussed: the distal extremity of the His bundle after the origin of part or all of the left posterior fascicle. This study, in its clinical and epidemiological context, demonstrates an inherited disease with both typical and "forme fruste" expressions. Compared with other series, it suggests the diverse nature of hereditary and familial conduction defects.