BIPOLAR-II - THE MOST COMMON BIPOLAR PHENOTYPE

Objective: The purpose of this study was to compare the pattern of aff ective psychopathology in families ascertained for genetic linkage stu dies through bipolar I probands to that in families ascertained throug h bipolar II probands. Method: All available first-degree relatives (N =266) of 48 bipolar I and eight bipolar II probands were interviewed w ith the Schedule for Affective Disorders and Schizophrenia-Lifetime Ve rsion by one of two psychiatrists who had attained high interrater rel iability for bipolar II disorder and other diagnoses. Results: Bipolar II disorder was the most common affective disorder in both family set s. Forty percent of the 47 first-degree relatives of the bipolar II pr obands and 22% of the 219 first-degree relatives of the bipolar I prob ands were diagnosed with bipolar II disorder. On the other hand, only one bipolar I relative was found in the bipolar II families. Conclusio ns: Bipolar II disorder was the most prevalent affected phenotype in b oth bipolar I and bipolar II families and was the only expressed pheno type in half of the bipolar II families. This suggests that bipolar II disorder is genetically related to but less complex than bipolar I di sorder. Accurate diagnosis of bipolar II disorder may be crucial in fi nding the genetic loci underlying bipolar disorders generally.