Familial amyloidotic polyneuropathy is due to amyloidosis of nerves caused by deposition of :
**Core Concept**
Familial amyloidotic polyneuropathy (FAP) is a rare genetic disorder characterized by the deposition of abnormal proteins in the peripheral nerves, leading to progressive neuropathy. This condition is caused by mutations in genes encoding for transthyretin (TTR), a transport protein primarily produced in the liver.
**Why the Correct Answer is Right**
The correct answer is related to the pathophysiology of FAP, which involves the accumulation of mutated TTR proteins in the peripheral nerves. This occurs due to the reduced clearance of these abnormal proteins by the liver, leading to their deposition in the nerves and subsequent damage to the nerve tissue. The deposition of amyloid fibrils composed of mutated TTR proteins disrupts the normal functioning of the nerves, resulting in the characteristic symptoms of FAP.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not specify the protein responsible for FAP. While amyloidosis is indeed a key feature of FAP, the specific protein involved is TTR.
**Option B:** This option is incorrect because it does not accurately describe the protein responsible for FAP. Transthyretin (TTR) is a transport protein, not a structural protein like collagen.
**Option C:** This option is incorrect because it does not specify the protein responsible for FAP. While amyloidosis is indeed a key feature of FAP, the specific protein involved is TTR.
**Clinical Pearl / High-Yield Fact**
It's essential to remember that FAP is caused by mutations in the TTR gene, which leads to the deposition of amyloid fibrils composed of mutated TTR proteins in the peripheral nerves. This is distinct from other forms of amyloidosis, such as Alzheimer's disease, where amyloid deposits are composed of beta-amyloid peptides.
**Correct Answer: D. Transthyretin (TTR)**