Ripple effects of developmental disabilities and mental illness on nondisabled adult siblings.

Developmental disabilities and severe mental illness are costly to the affected individual and frequently to their family as well. Little studied are their nondisabled siblings. Here we examine major life course outcomes (education, employment, and marriage) of these siblings in adulthood using data from the Wisconsin Longitudinal Study. Our sample comprises 113 individuals with developmental disabilities and 337 of their nondisabled siblings; 97 individuals with mental illness and 235 of their nondisabled siblings; and 17,126 unaffected comparison group members. We find that siblings of individuals with mental illness have less education and less employment than the unaffected comparison group, whereas those who have a sibling with developmental disabilities had normative patterns of education and employment, but less marriage and more divorce. Robustness tests incorporating genetic data do not change the conclusions based on the nongenetic analyses.