Involved in the maturation of specific proteins in the endoplasmic reticulum. Required for maturation and transport of active lipoprotein lipase (LPL) through the secretory pathway. Each LMF1 molecule chaperones 50 or more molecules of LPL. Interacts with LPL and SEL1L. Expressed in all tissues synthesizing lipoprotein lipase (Lpl) and hepatic lipase (Lipc), including adipose tissue, skeletal muscle, heart, and liver. Expressed at higher levels in tissues that express little or no lipase activity such as testis and pancreas suggesting additional functions in these tissues. Defects in Lmf1 are the cause of combined lipase deficiency (cld). Cld is characterized by severe hypertriglyceridemia with accumulation of chylomicrons that gradually pack the lumina of capillaries and sinusoids. Severe hypertriglyceridemia causes an increase in blood viscosity, ischemia, and cyanosis, and the inability of tissues to access circulating triglycerides results in starvation, poor thermoregulation, and death 2 to 3 days after birth. The disorder is caused by a decrease in the activity of lipoprotein lipase (Lpl) and the related hepatic lipase (Lipc), caused by impaired maturation of nascent Lpl and hepatic lipase polypeptides in the endoplasmic reticulum. Belongs to the lipase maturation factor family. Additional evidence for its localization to the endoplasmic reticulum membrane was found. However this paper was retracted due to manipulation of data.