What is deficient in Tangier's disease, a familial hypocholesterolemia?

Tangier's disease is characterized by a deficiency of Apolipoprotein A-I (Apo A-I), which is crucial for the normal metabolism of lipoproteins. Apo A-I is an essential component of high-density lipoprotein (HDL), often referred to as "good cholesterol," and it plays a significant role in the reverse transport of cholesterol from peripheral tissues back to the liver.

In individuals with Tangier's disease, the absence or malfunction of Apo A-I leads to dramatically reduced levels of HDL cholesterol and impaired cholesterol transport. As a result, patients often present with hypocholesterolemia and other related symptoms. The accumulation of cholesterol in tissues can lead to distinctive clinical features such as orange tonsils and peripheral neuropathy.

Understanding the role of Apo A-I in lipid metabolism reinforces its significance in conditions like Tangier's disease, highlighting why its deficiency is central to the pathology of this disorder.