**Question:** Tangier disease is characterized by

A. Abnormal cholesterol transport
B. Increased intestinal cholesterol absorption
C. Decreased high-density lipoprotein (HDL) cholesterol
D. Altered low-density lipoprotein (LDL) cholesterol

**Core Concept:** Tangier disease is a rare autosomal recessive disorder affecting cholesterol and phospholipid homeostasis. It is characterized by a deficiency in the ATP-binding cassette (ABC) transporter ABCA1, which plays a crucial role in the cellular process of cholesterol efflux and the formation of high-density lipoprotein (HDL) particles.

**Why the Correct Answer is Right:** Tangier disease results in decreased cholesterol efflux from cells, leading to hypoalphalipoproteinemia (low HDL cholesterol) and increased cholesterol accumulation in macrophages, hepatocytes, and other tissues. This accumulation leads to various clinical manifestations, such as peripheral neuropathy, hepatomegaly, and osteoporosis.

**Why Each Wrong Option is Incorrect:**

A. **Incorrect** - Tangier disease primarily affects HDL cholesterol levels, not LDL cholesterol.

B. **Incorrect** - Increased intestinal cholesterol absorption does not describe the underlying pathophysiology of Tangier disease.

C. **Incorrect** - Tangier disease primarily affects HDL cholesterol levels, not LDL cholesterol.

D. **Incorrect** - Tangier disease primarily affects HDL cholesterol levels, not altered LDL cholesterol.

**Clinical Pearl:** Tangier disease is an example of a monogenic disorder of lipid and lipoprotein homeostasis, emphasizing the importance of ABCA1 function in maintaining cholesterol and phospholipid levels within cells and extracellularly. A clinical understanding of lipid disorders helps in diagnosing and managing patients with similar presentations and guiding further genetic testing.