APOB and familial hypobetalipoproteinemia 1: In contrast, familial hypobetalipoproteinemia (FHBL) is mainly caused by protein-truncating variants in the APOB gene, resulting in reduced production of apolipoprotein B100 and its assembly with triglyceride, cholesterol and lipoprotein, causing a very low secretion of cholesterol from hepatocyte into blood circulation33.