Objective: Familial risks of depression have been assessed in small case-control studies, usually based on reported, but not medically verified, depressions in family members; thus the degree of familial clustering of these diseases remains to be established.
Methods: The Multigeneration Register, in which all men and women born in Sweden from 1932 onward are registered together with their parents, was linked to hospital admission data. Standardized incidence ratios (SIRs) were calculated as the ratio of the observed to the expected number of cases in men and women with mothers or fathers affected by depression, compared with men and women whose mothers or fathers were not affected by depression.
Results: A total of respectively 60,477 and 79,969 depressions were recorded in offspring and parents. In 6.44% of all families, an offspring and a parent were affected, giving a population-attributable proportion of 4.04% and a familial SIR of 2.68. The parental transmission of depression was similar for both men and women (2.72 and 2.66).
Conclusions: This study has provided the first data on age-specific familial clustering of depressions, based on medically confirmed records. The risks were so high that hereditary factors were considered to be likely to contribute to depression, possibly modified by environmental factors. Age-specific risk tables would be helpful for clinical counseling.