Albinism is due to deficiency of
**Core Concept**
Albinism is a group of rare genetic disorders characterized by the complete or partial absence of melanin production in the skin, hair, and eyes. This condition is usually inherited in an autosomal recessive pattern and affects the function of melanocytes, the cells responsible for producing melanin.
**Why the Correct Answer is Right**
Albinism is primarily due to mutations in the genes responsible for encoding enzymes involved in the melanin synthesis pathway. The most common form of albinism, oculocutaneous albinism type 1 (OCA1), is caused by mutations in the TYR gene, which encodes the enzyme tyrosinase. Tyrosinase catalyzes the conversion of the amino acid tyrosine to melanin. Without functional tyrosinase, melanin production is severely impaired, leading to the characteristic features of albinism.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because albinism is not caused by a deficiency of vitamin B12, which is involved in the synthesis of myelin and the metabolism of fatty acids.
**Option B:** This option is incorrect because albinism is not caused by a deficiency of melanin itself, but rather by the inability to produce melanin due to genetic mutations.
**Option C:** This option is incorrect because albinism is not caused by a deficiency of the enzyme phenylalanine hydroxylase, which is involved in the metabolism of the amino acid phenylalanine.
**Clinical Pearl / High-Yield Fact**
It's essential to note that albinism is not a single disorder, but rather a group of genetic conditions that affect melanin production. Each type of albinism has distinct clinical features and is caused by mutations in specific genes involved in the melanin synthesis pathway.
**Correct Answer:** D. TYR gene mutations