APOL1, also known as apolipoprotein L1, is a minor apoprotein component of HDL (High-density lipoprotein) or 'good cholesterol' which is synthesized in the liver and also in many other tissues, including pancreas, kidney, and brain. APOL1 belongs to the apolipoprotein L family. It may play a role in lipid exchange and transport throughout the body. It may also participate in reverse cholesterol transport from peripheral cells to the liver. Defects in APOL1 are the cause of focal segmental glomerulosclerosis type 4 (FSGS4). It is a renal pathology defined by the presence of segmental sclerosis in glomeruli and resulting in proteinuria, reduced glomerular filtration rate and edema. Renal insufficiency often progresses to end-stage renal disease, a highly morbid state requiring either dialysis therapy or kidney transplantation.