Lithium ratio in vitro: familial patterns of illness.

Psychiatric illness in first-degree relatives of psychotic patients with low, intermediate, and high red blood cell (RBC) in vitro lithium ratio (LR) was investigated using the Schedule for Affective Disorders and Schizophrenia and DSM-III. Fewer schizophrenic spectrum disorders were found in the first-degree relatives of high and low LR probands as compared to intermediate LR probands; high LR psychotic probands had families with an increased frequency of depressive spectrum disorder. Alcohol dependence and abuse was particularly prominent in the first-degree relatives of the higher LR probands. High LR may identify a disease that does not belong to the familial-genetic disorders of the schizophrenic spectrum; this illness may bear a closer relationship to disorders of the depressive spectrum.