The search for genetic homogeneity in affective disorders.

In the present study we tested the fit of the Single Major Locus (SML) hypothesis, using segregation analysis for single families of affective probands treated with lithium salts, with second degree relatives included. We tested the segregation pattern for every family with two different sets of parameters: one dominant for a group that did not relapse on lithium treatment and one recessive for a group that did. We calculated the likelihood ratios for each family. The results of this study partially confirm the importance of outcome on lithium treatment in susceptibility to affective disorders. However, application of segregation analysis suggested that there is genetic heterogeneity that cannot be completely detected when using only the simple pharmacological criterion of outcome on lithium.