**Question:** 'I' cells disease is due to defect in:-

A. Copper transporter 1 (CTR1)
B. Zinc transporter 3 (ZnT3)
C. Zinc transporter 8 (ZnT8)
D. Zinc-alpha2-glycoprotein (AZGP1)

**Correct Answer:** .

**Core Concept:**
I cells disease, also known as Wilson-Konovalov syndrome, is a rare autosomal recessive disorder characterized by copper overload in tissues and organs, leading to liver disease, neuropathy, and hypogonadism. This condition is caused by mutations in the ATP7B gene, which encodes for a protein called copper transporter 1 (CTR1).

**Why the Correct Answer is Right:**
I cells disease results from a deficiency in copper transporter 1 (CTR1), which is responsible for copper uptake into the liver cells. Mutations in the ATP7B gene lead to a reduced number or function of CTR1 proteins, impairing liver copper uptake and causing excessive copper accumulation in other organs. This copper overload triggers liver disease, neuropathy, and hypogonadism.

**Why Each Wrong Option is Incorrect:**

A. Copper transporter 1 (CTR1) is the correct answer, as it is involved in copper uptake into liver cells. Mutations in ATP7B gene lead to reduced CTR1 function in Wilson-Konovalov syndrome. Therefore, option A is incorrect.

B. Zinc transporter 3 (ZnT3) is responsible for zinc transport in neurons and not copper transport, making option B incorrect.

C. Zinc transporter 8 (ZnT8) is involved in zinc transport in pancreatic beta cells and is not related to copper transport or Wilson-Konovalov syndrome, making option C incorrect.

D. Zinc-alpha2-glycoprotein (AZGP1) is a protein involved in zinc homeostasis and not copper transport, making option D incorrect.

**Clinical Pearl:**
Understanding the correct answer and reasons behind incorrect options is crucial for diagnosing Wilson-Konovalov syndrome in suspected cases and providing appropriate treatment options for patients with this condition.