**Question:** Wilson disease is caused by defect in

A. ATP7B
B. copper transport proteins
C. copper reabsorption proteins
D. copper excretion proteins

**Correct Answer:** A. ATP7B

**Core Concept:** Wilson disease is a rare genetic disorder characterized by excess copper accumulation in liver, brain, and other tissues. It is caused by mutations in the ATP7B gene, which encodes for the copper transporter protein called ATP7B. This protein plays a crucial role in the transport and excretion of copper from the liver and other tissues.

**Why the Correct Answer is Right:** ATP7B is a copper-transporting P-type ATPase protein that helps in the transport of copper across cellular membranes. In Wilson disease, mutations in the ATP7B gene lead to a reduction or loss of function of ATP7B. As a result, copper is not efficiently transported out of the liver cells and is accumulated within the cells. This excess copper can cause severe liver damage, neurological symptoms, and other complications.

**Why Each Wrong Option is Incorrect:**

**Option A (B):** Copper transport proteins (B) refers to a more general category that ATP7B belongs to. However, the correct answer is ATP7B specifically, as it is the defective gene/protein causing Wilson disease.

**Option B (Copper reabsorption proteins):** Copper reabsorption proteins are unrelated to Wilson disease. Copper reabsorption occurs in the gastrointestinal tract, and ATP7B is involved in copper excretion, not reabsorption.

**Option C (Copper excretion proteins):** Similar to Option B, copper excretion proteins are involved in removing copper from the body, not accumulating it as in Wilson disease. Wilson disease is caused by an inability to excrete copper, not increase it.

**Core Concept (Wilson disease pathogenesis):** Wilson disease is a genetic disorder resulting from mutations in the ATP7B gene, which encodes for ATP7B, a protein involved in copper transport and excretion. When ATP7B function is impaired, copper accumulates in the liver and other tissues, leading to liver damage, neurological symptoms, and other complications.

**Clinical Pearl:** Wilson disease highlights the importance of understanding the role of ATP7B and copper transport in maintaining copper homeostasis within the body. This is crucial for recognizing and managing patients with copper-related disorders, including Wilson disease and Menkes disease. Adequate understanding of these genetic disorders can help in proper diagnosis and treatment planning, ultimately improving patient outcomes.