A 1-year-old boy with pale hair and blue eyes cries when exposed to light. The pale skin color is most likely due to which mechanism?

A 1-year-old boy with pale hair and blue eyes cries when exposed to light. The pale skin color is most likely due to which mechanism?

• A. Inability to produce melanin
• B. Increased melanin production
• C. Excess carotene accumulation
• D. Increased tyrosinase activity

Answer: (A)

Pale hair, blue eyes, and photophobia point to albinism, a direct problem with melanin synthesis in melanocytes. Melanin is produced from tyrosine through a process that requires the enzyme tyrosinase; when this pathway is defective, melanin cannot be made, leading to very light skin and hair and increased light sensitivity due to lack of pigment in the iris and retina. Thus the skin color change is best explained by an inability to produce melanin. Increased melanin production would darken skin, excess carotene causes an orange tint, and increased tyrosinase activity would raise melanin, not reduce it.

Pale hair, blue eyes, and photophobia point to albinism, a direct problem with melanin synthesis in melanocytes. Melanin is produced from tyrosine through a process that requires the enzyme tyrosinase; when this pathway is defective, melanin cannot be made, leading to very light skin and hair and increased light sensitivity due to lack of pigment in the iris and retina. Thus the skin color change is best explained by an inability to produce melanin. Increased melanin production would darken skin, excess carotene causes an orange tint, and increased tyrosinase activity would raise melanin, not reduce it.