In the hope of throwing light on the genetic problem of affective illness of later life, 100 in-patients over the age of fifty were studied.
Thirty-nine of these patients had experienced attacks before the age of 50, and 61 had a first attack after this age.
Clinically these two groups resembled each other closely.
The morbidity risk for affective illness in all first degree relatives was calculated. This risk was as follows: 14.5±2 per cent. for relatives of all patients; 20.1±3.6 per cent. for relatives of early onset probands; 8.3±1.9 per cent. for relatives of late onset probands. The risk for affective illness in relatives of probands diagnosed as involutional melancholia is 10.2± 3.4 per cent.
The incidence of schizophrenia in first degree relatives does not exceed the normal expectation in any of the subgroups mentioned above.
The significance of these findings is discussed.