The 113 probands with bipolar disorder characterized by alternating episodes of depression were identified as caused by various homozygous as well as heterozygous mutations in DSEL, such as the substitution of adenine to guanine in the 5′-non-coding region 546 bp upstream of the coding region, p.Val287Ile, p.Pro673Ser, p.Tyr730Cys, p.Pro942Ser, and p.Ile1113Met, in DSEL (Table 2; Goossens et al., 2003). Here, DSEL is linked to major depressive disorder.