Linkage studies of bipolar disorder: methodologic and analytic issues. Report of MacArthur Foundation Workshop on Linkage and Clinical Features in Affective Disorders.

To review the findings of the linkage studies of affective disorders, a workshop, "Linkage and Clinical Features in Affective Disorders," was organized by the MacArthur Foundation Mental Health Research Network I on the Psychobiology of Depression meeting in Alexandria, Va, April 13 to 15, 1989. The major goals of the workshop for affective disorders were to explore the relationship between genetic and clinical heterogeneity, to identify major impediments to linkage studies, and to develop recommendations for the application of standardized methods of conducting linkage studies. The participants in the conference presented detailed demographic and clinical data from most of the published linkage studies of affective disorders. No systematic correspondence between genetic and clinical subtypes of bipolar disorder pedigrees was evident. The major problems hampering the linkage analyses of psychiatric disorders that were identified follow: (1) the major psychiatric disorders--the affective disorders in particular--constituting complex human disorders; (2) the lack of valid definitions of affective disorders; (3) comorbidity between the affective disorders with other disorders; (4) nonrandom mating; (5) a cohort effect, with younger birth cohorts exhibiting higher rates of affective disorders; and (6) the lack of replication of current linkage studies. The recommendations that were made for linkage study designs that incorporate some of the complexities of the affective disorders are reported.