Which of the following result from accumulation of homogentisic acid?
**Core Concept**
Accumulation of homogentisic acid leads to a condition characterized by the breakdown of the amino acid tyrosine. This results from a deficiency in the enzyme homogentisate 1,2-dioxygenase (HGD), which is crucial in the tyrosine catabolic pathway.
**Why the Correct Answer is Right**
Homogentisic acid is a toxic intermediate that accumulates due to the impaired activity of HGD. Normally, HGD catalyzes the oxidation of homogentisic acid to maleylacetoacetic acid, thereby preventing its accumulation. In the absence of functional HGD, homogentisic acid builds up and causes cellular damage, leading to the development of alkaptonuria. This condition is associated with the ochronosis (bluish-black pigmentation) of cartilages and connective tissues.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not directly relate to the accumulation of homogentisic acid. While it may be a condition affecting the skin, it is not the primary result of homogentisic acid accumulation.
**Option B:** This option is incorrect because it refers to a different metabolic disorder, one involving the accumulation of phenylpyruvic acid due to a deficiency in phenylalanine hydroxylase.
**Clinical Pearl / High-Yield Fact**
Alkaptonuria is an autosomal recessive disorder, and patients often present with dark urine and a history of joint pain in adulthood. The condition can be diagnosed by demonstrating the presence of homogentisic acid in the urine.
**Correct Answer:** C. Alkaptonuria