The present invention relates to compositions and methods for the diagnosis and treatment of obesity and related metabolic disorders. The invention provides isolated nucleic acids molecules, designated DGAT2 family member nucleic acid molecules, which encode diacylglycerol acyltransferase family members. The invention also provides recombinant expression vectors containing DGAT2 family member nucleic acid molecules, host cells into which the expression vectors have been introduced, and nonhuman transgenic animals in which a DGAT2 family member gene has been introduced or disrupted. The invention still further provides isolated DGAT2 family member proteins, fusion proteins, antigenic peptides and anti-DGAT2 family member antibodies. Methods of use of the provided DGAT2 family member compositions for screening, diagnostic and therapeutic methods in connection with obesity disorders are also disclosed.