Factors affecting the distribution of age at onset in patients with affective disorders.

We analyzed the age-at-onset distributions in a group of 285 patients diagnosed as having major affective disorder, recurrent, either unipolar or bipolar, in order to detect the possible existence of genetic and epidemiological factors affecting their age-at-onset distribution. In fact, since it is known that affective disorders are genetically heterogeneous with respect to the liability systems involved, methodological considerations support the hypothesis of the existence of different ages at onset also. We thus investigated several variables and the significant findings of our study were that bipolarity, at least one affected parent and a low position in the sibship are each associated with earlier age at onset of affective disease.