To the Editor.—Early research suggesting X-linked dominant transmission of some forms of bipolar illness was a stimulus for further investigation. Conflicting results of subsequent linkage studies, however, has led to a divergence of opinion about this mode of transmission. To provide an additional perspective on the complex task of determining whether such transmission of bipolar illness indeed exists, I will describe established X-linked dominant disorders in relation to our growing understanding of X-chromosome inactivation.
Winokur et al1 reported a withinpedigree association of affective disorders with the X-linked markers of protan and deutan color blindness and with the Xg blood group. (X-linked markers are traits controlled by genes that are located on the X chromosome.) Their study was a harbinger of a number of X-linkage studies on pedigrees identified by a member with bipolar illness,2,3 some providing evidence for X-linked dominant transmission of bipolar illness, and others not. Discussions of these