Definition and Characteristics
Hypocholesterolemia (HC) is either primary or secondary. Secondary and nonfamilial causes of HC include a high catabolic state (malignancy, chronic liver disease, anorexia, hyperthyroidism, etc), malabsorption, intense dieting, lipid lowering medications and a primitive hunter-gatherer lifestyle. Primary hypocholesterolemia (PHC) includes primary hypobetalipoproteinemia (PHBL), which is a heterogeneous group of inherited disorders characterized by very low plasma level (<5th percentile of the distribution in the population) of low density lipoprotein–cholesterol (LDL-C) and apolipoprotein B (ApoB). PHBL has three subgroups: abetalipoproteinemia (ABL), familial hypobetalipoproteinemia (FHBL), and chylomicron retention disease (CRD). Tangier disease (TGD) is also a cause of PHC with a mean plasma total cholesterol (TC) of 1.75 ± 0.35 mmol/L. Patients with TGD have very low apolipoprotein AI (apo AI) and high density lipoprotein–cholesterol (HDL-C), with...