Ochronosis is seen in poisoning with: DNB 09; FMGE 11; NEET 13
**Core Concept**
Ochronosis is a bluish-black pigmentation of connective tissue, typically seen in the skin, cartilage, and other tissues. It results from the accumulation of homogentisic acid, a metabolite of tyrosine catabolism. This condition is associated with a genetic disorder affecting the enzyme responsible for breaking down tyrosine.
**Why the Correct Answer is Right**
The correct answer involves the deficiency of homogentisate 1,2-dioxygenase (HGD), an enzyme crucial for the degradation of homogentisic acid. Without HGD, homogentisic acid accumulates and polymerizes, leading to the formation of a pigment called alkapton. This pigment is responsible for the characteristic bluish-black coloration seen in ochronosis. The condition is inherited in an autosomal recessive manner and is known as alkaptonuria.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because ochronosis is not primarily associated with lead poisoning, which causes a different type of pigmentation.
* **Option B:** This option is incorrect because phenol is not directly linked to ochronosis, which is specifically related to the accumulation of homogentisic acid.
* **Option C:** This option is incorrect because mercury poisoning does not cause ochronosis; it can lead to other types of skin and mucous membrane lesions.
**Clinical Pearl / High-Yield Fact**
Ochronosis can lead to joint degeneration and other complications due to the accumulation of homogentisic acid in connective tissues.
**Correct Answer: D. Alkaptonuria**