Normal intravascular lipolysis (A), lipolysis in the setting of a GPIHBP1 missense mutation in the LU domain (B), or in the presence of GPIHBP1 autoantibodies (autoAbs) (C). Absent GPIHBP1 function, caused either by a GPIHBP1 missense mutation or GPIHBP1 autoAbs, eliminates transport of LPL to the capillary lumen, causing a dramatic reduction in intravascular triglyceride hydrolysis and severe hypertriglyceridemia (chylomicronemia).