**Core Concept**
Calcification of intervertebral discs is a rare condition that can be associated with various metabolic disorders. It is characterized by the deposition of calcium salts within the disc, leading to changes visible on radiographs.

**Why the Correct Answer is Right**
Alkaptonuria is a rare inherited metabolic disorder caused by the deficiency of homogentisate 1,2-dioxygenase enzyme. This enzyme is essential for the breakdown of tyrosine and phenylalanine. In alkaptonuria, the accumulation of homogentisic acid (HGA) leads to its oxidation and subsequent polymerization, resulting in the formation of a pigment called melanin-like substance. This pigment is deposited in various tissues, including cartilage, leading to calcification of intervertebral discs, as seen in the condition known as ochronosis. The calcification of intervertebral discs in alkaptonuria is due to the deposition of calcium salts in the previously mentioned cartilaginous matrix, which is disrupted by the accumulation of HGA.

**Why Each Wrong Option is Incorrect**
**Option A:** Gout is a metabolic disorder characterized by the deposition of monosodium urate crystals in joints, but it is not associated with calcification of intervertebral discs.

**Option B:** Rheumatoid arthritis is an autoimmune disorder that primarily affects the synovial joints, causing inflammation and destruction of cartilage and bone. It is not typically associated with calcification of intervertebral discs.

**Option D:** Psoriasis is a chronic autoimmune skin disorder that can also affect joints, but it is not associated with calcification of intervertebral discs.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that calcification of intervertebral discs can be a feature of various metabolic disorders, and a thorough medical history is crucial in diagnosing the underlying condition.

**✓ Correct Answer: C. Alkaptonuria**