Humans lipodystrophy is characterized by loss of body fat, fatty liver, hypertriglyceridemia, and insulin resistance. Mice carrying mutations in the fatty liver dystrophy (fld) gene have similar phenotypes. Through positional cloning, the mouse gene responsible for fatty liver dystrophy was isolated and designated Lpin1. The nuclear protein encoded by Lpin1 was named lipin. Lpin1 mRNA was expressed at high levels in adipose tissue and was induced during differentiation of preadipocytes. These results indicated that lipin is required for normal adipose tissue development and provided a candidate gene for human lipodystrophy. Through database searches, mouse and human EST and genomic sequences with similarities to Lpin1 were identified. These included two related mouse genes (Lpin2 and Lpin3) and three human homologs (LPIN1, LPIN2, and LPIN3). Human LPIN1 gene has been mapped to 2p25.\; linkages of fat mass and serum leptin levels to this same region have been noted. Human LPIN2 and LPIN3 mapped to chromosomes 18p11 and 20q11-q12, respectively. The mouse genes encoding Lpin1, Lpin2, and Lpin3 mapped to chromosome 12, 17, and 2, respectively.