Fat specific protein 27 (FSP27) was originally isolated by screen for genes 
specifically expressed in fully differentiated mouse adipocytes. FSP27 and cell 
death-inducing DFF45-like effector C (CIDEC), the human homologue of FSP27, 
belong to the CIDE family. The FSP27 in adipocytes was recently reported to be a 
lipid droplet (LD)-associated protein, that promotes the formation of unilocular 
LDs. An FSP27 knockout mouse demonstrated lean phenotypes with atrophic adipose 
tissue as a result of high-energy expenditure; this mouse line was also 
resistant to diet-induced obesity and insulin resistance. Interestingly, FSP27 
was also expressed in the steatoic liver of a type II diabetes model mouse. The 
expression of FSP27 was markedly decreased in livers lacking the nuclear 
receptor peroxisome proliferator-activated receptor gamma. Forced expression of 
FSP27 in hepatocytes in vitro or in vivo led to an increase of LD through 
increased triglyceride levels. The current status of the physiological roles of 
FSP27/CIDEC in adipose tissue and liver are discussed along with its 
significance as a factor involved in the development of metabolic disorders.