Family study of subthreshold psychopathology in a community sample

There has been increasing interest in the validity and familial transmission of subthreshold psychiatric conditions and the relationship between subthreshold conditions and full syndrome (FS) disorders. However, most of these studies examined a single subthreshold condition and thus fail to take into account the high co-morbidity among subthreshold conditions and between subthreshold conditions and FS disorders.

A family study of subthreshold psychiatric conditions was conducted with 739 community-drawn young adults and their 1744 relatives. We examined (1) whether relatives of probands with subthreshold major depression, bipolar disorder, anxiety disorders, alcohol use, substance use, and/or conduct disorder exhibited an increased rate of the corresponding (homotypic) FS disorder; (2) whether subthreshold disorders were associated with increased familial rates of other (heterotypic) FS disorders; (3) whether subthreshold and FS conditions are associated with similar familial liabilities; and (4) whether these homotypic and heterotypic associations persisted after controlling for co-morbidity.

Significant homotypic associations were observed for subthreshold anxiety, alcohol, conduct, and a trend was observed for major depression. Only the homotypic association for alcohol and conduct remained after controlling for co-morbid subthreshold and FS conditions. Many heterotypic associations were observed and most remained after controlling for co-morbidity.

It is important to broaden the study of subthreshold psychopathology to multiple disorders. In particular cases, controlling for co-morbidity with other subthreshold and FS conditions altered the patterns of familial aggregation. Etiological processes that are common to particular disorders and subthreshold conditions are discussed.