All are TRUE about amyloidosis, EXCEPT:
**Core Concept**
Amyloidosis is a group of disorders characterized by the extracellular deposition of amyloid fibrils, which are composed of insoluble, fibrillar proteins. The deposition of amyloid fibrils can disrupt tissue architecture and function, leading to various clinical manifestations.
**Why the Correct Answer is Right**
Amyloidosis can be primary (idiopathic) or secondary (associated with chronic diseases such as rheumatoid arthritis, tuberculosis, or multiple myeloma). The deposition of amyloid fibrils is mediated by the misfolding of proteins, which are then aggregated and deposited in tissues. The amyloid fibrils can be composed of various proteins, including immunoglobulin light chains (in primary amyloidosis), transthyretin (in familial amyloid polyneuropathy), or amyloid A protein (in secondary amyloidosis).
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because amyloidosis can indeed cause renal failure, as the deposition of amyloid fibrils can disrupt renal function and lead to chronic kidney disease.
**Option B:** This option is incorrect because amyloidosis is associated with a variety of clinical manifestations, including cardiomyopathy, neuropathy, and gastrointestinal symptoms.
**Option C:** This option is incorrect because amyloidosis is characterized by the deposition of amyloid fibrils in various tissues, including the skin, tongue, and gastrointestinal tract.
**Clinical Pearl / High-Yield Fact**
The diagnosis of amyloidosis often requires a combination of clinical evaluation, laboratory tests (including serum and urine protein electrophoresis), and tissue biopsy. A key feature of amyloidosis is the presence of a "lattice" or "pseudogranular" appearance of amyloid fibrils on electron microscopy.
**Correct Answer: D.**