Which enzyme defect leads to albinism?

The correct answer is the enzyme tyrosinase, which plays a crucial role in the production of melanin, the pigment responsible for the color of skin, hair, and eyes. Albinism is characterized by a deficiency or complete lack of melanin due to mutations in the gene encoding tyrosinase. This enzyme is essential for the conversion of the amino acid tyrosine into melanin through a series of steps in the melanin biosynthetic pathway. When tyrosinase is absent or not functioning properly, melanin production is significantly reduced, resulting in the clinical manifestations of albinism, which include hypopigmented skin, hair, and eyes, as well as increased sensitivity to sunlight and a higher risk of skin cancer.

In contrast, the other enzymes listed have roles in different metabolic pathways and are associated with other conditions. Homogentisic acid oxidase is involved in the metabolism of phenylalanine and tyrosine, specifically in alkaptonuria. Branched-chain alpha-keto acid dehydrogenase is linked to maple syrup urine disease, affecting the metabolism of branched-chain amino acids. Phenylalanine hydroxylase is the enzyme deficient in phenylketonuria (PKU),