Introduction
Twin, family, and adoption studies of bipolar (BP)
disease are consistent with complex (non-Mendelian)
inheritance. Heritability estimates (from twin studies)
of BP illness vary from ~60 to 80%. In an effort
to localize susceptibility genes from BP disorder, 22
multiplex BP kindreds were genotyped for DNA markers
spanning the human genome. Evidence for susceptibility
loci on chromosomes 18p and 21q is presented below.