A 15-year-old girl is seen by a dermatologist for removal of multiple squamous cell carcinomas of the skin. The patient has nearly white hair, pink irises, very pale skin, and a history of burning easily when exposed to the sun. This patient's condition is caused by a disorder involving which of the following substances?

A. Aromatic amino acids
B. Branched chain amino acids
C. Glycolipids
D. Glycoproteins
E. Sulfur-containing amino acids

A.

The correct answer is A. The disease is albinism. The most common form of albinism is caused by a deficiency of copper-dependent tyrosinase (tyrosine hydroxylase), blocking the production of melanin from the aromatic amino acid tyrosine. Affected individuals lack melanin pigment in skin, hair, and eyes, and are prone to develop sun-induced skin cancers, including both squamous cell carcinomas and melanomas.
Maple syrup urine disease is an example of a disorder of branched chain amino acids (choice B) causing motor abnormalities and seizures.

Tay-Sachs disease is an example of a disorder of glycolipids (choice C). In this disorder, a deficiency of hexosaminidase A leads to accumulation of ganglioside GM2.

Hunter's disease is an example of a disorder of glycoproteins (choice D). This mucopolysaccharidosis is inherited as an X-linked recessive trait.

Homocystinuria disease is an example of a disorder of sulfur-containing amino acids (choice E).