Triglyceride (TG) synthesis, storage, and degradation together constitute 
cytoplasmic TG metabolism (CTGM). CTGM is mostly studied in adipocytes, where 
starting from glycerol-3-phosphate and fatty acyl (FA)-coenzyme A (CoA), TGs are 
synthesized then stored in cytoplasmic lipid droplets. TG hydrolysis proceeds 
sequentially, producing FAs and glycerol. Several reactions of CTGM can be 
catalyzed by more than one enzyme, creating great potential for complex 
tissue-specific physiology. In adipose tissue, CTGM provides FA as a systemic 
energy source during fasting and is related to obesity. Inborn errors and mouse 
models have demonstrated the importance of CTGM for non-adipose tissues, 
including skeletal muscle, myocardium and liver, because steatosis and 
dysfunction can occur. We discuss known inborn errors of CTGM, including 
deficiencies of: AGPAT2 (a form of generalized lipodystrophy), LPIN1 (childhood 
rhabdomyolysis), LPIN2 (an inflammatory condition, Majeed syndrome, described 
elsewhere in this issue), DGAT1 (protein loosing enteropathy), perilipin 1 
(partial lipodystrophy), CGI-58 (gene ABHD5, neutral lipid storage disease 
(NLSD) with ichthyosis and "Jordan's anomaly" of vacuolated polymorphonuclear 
leukocytes), adipose triglyceride lipase (ATGL, gene PNPLA2, NLSD with myopathy, 
cardiomyopathy and Jordan's anomaly), hormone-sensitive lipase (HSL, gene LIPE, 
hypertriglyceridemia, and insulin resistance). Two inborn errors of glycerol 
metabolism are known: glycerol kinase (GK, causing pseudohypertriglyceridemia) 
and glycerol-3-phosphate dehydrogenase (GPD1, childhood hepatic steatosis). 
Mouse models often resemble human phenotypes but may diverge markedly. Inborn 
errors have been described for less than one-third of CTGM enzymes, and new 
phenotypes may yet be identified.