[Clinical and molecular genetics of familial bundle branch block related to chromosome 19].

Four large Lebanese families were observed for several years and over several generations which enabled the authors to describe the clinical electrocardiographic and prognostic features of a hereditary conduction defect and to locate the culprit gene at 19q 13.3. The ECG showed a healthy group and an affected group (mainly right bundle branch block, hemiblocks or complete AV block) and an undetermined group with minor QRS changes in the right precordial leads. The mode of transmission was autosomal dominant. The estimation of penetration in the observed pedigrees and in previously published pedigrees gave a value of 70% in men and 50% in women. There were, therefore, many healthy carriers of the mutation. The onset was congenital (8 babies aged 15 days to one year were affected). Healthy carriers followed up for 10 to 20 years remained normal. The clinical and ECG features progressed in 19% of subjects in the undetermined group. The changes progressed to complete AV block in 8% of affected subjects, both babies and adults. Several cases of sudden infant death were reported but were not documented. The detection of the culprit gene was made by genetic mapping. Markers situated at q 13.3 on chromosome 19 showed linkage. The haplotype related to the pathology was always present in the affected subjects. The genetic interval was 7 centiMorgans.