Family history study on hypertension in Japan.

1. Familial aggregation of hypertension was determined in 187 Japanese nuclear families. The necessary data on family and case history particularly concerning the hypertensive status were obtained by personal interviews of outpatients at six local hospitals, using a specifically designed questionnaire. 2. From the family history of the 187 living index children (single ascertainment), 134 pairs of parents were informative. Of 819 children, excluding index cases, the number of hypertensives, normotensives and status unknown were 224, 274 and 187, respectively. Individuals under 30 were classified as unknown. 3. For a child given the birth order, empirical risk to be hypertensive was calculated from the proportion of hypertensives to normotensives plus hypertensives. 4. Irrespective of parental mating types, among a simplex family of hypertension the index cases of the first-born child were more than the others. 5. There was no birth order effect in risk among multiplex families of hypertension. 6. There was no increase of hypertensive offsprings observed when the mother was hypertensive.