Random Dermatology MCQs - Menkes kinky hair syndrome

A 6-month-old infant presents with silvery-blonde hair, failure to thrive, and seizures. Laboratory studies reveal low serum copper and ceruloplasmin levels. Which of the following is the most likely underlying defect?

A) Defective melanin synthesis
B) Mutation in the ATP7A gene
C) Deficiency of complement C3
D) Abnormal collagen type III production
E) Autoantibodies against desmoglein-1

Correct Answer: B) Mutation in the ATP7A gene

Explanation

This infant has Menkes kinky hair syndrome, an X-linked recessive disorder caused by mutations in ATP7A, which encodes a copper-transporting ATPase. Key features:

• Hypopigmented, friable hair ("kinky" or steel wool-like) due to defective cross-linking of keratin and melanin.

• Neurologic degeneration (seizures, hypotonia, developmental delay) from impaired copper-dependent enzymes (e.g., cytochrome c oxidase, dopamine β-hydroxylase).

• Low copper/ceruloplasmin due to defective intestinal absorption and transport.

Why not the others?

• (A) Melanin synthesis defects (e.g., albinism) cause hypopigmentation but not neurologic symptoms or low copper.

• (C) C3 deficiency causes recurrent infections, not hair/metabolic abnormalities.

• (D) Collagen III defects are seen in Ehlers-Danlos syndrome (vascular type).

• (E) Anti-desmoglein-1 antibodies cause pemphigus foliaceus (blistering).

Diagnostic clue: Punched-out "pili torti" on hair microscopy (flattened, twisted shafts). Treatment involves subcutaneous copper-histidine, but outcomes remain poor due to CNS damage.