Which inheritance pattern is characteristic of Bruton's agammaglobulinemia?

• A. X-linked recessive
• B. Autosomal recessive
• C. Autosomal dominant
• D. X-linked dominant

Answer: (A)

Bruton's agammaglobulinemia is inherited in an X-linked recessive pattern. The BTK gene on the X chromosome is mutated, blocking B-cell maturation. Since males have only one X chromosome, a single mutated BTK allele causes disease, while females are typically carriers and are rarely affected. This explains why affected individuals are predominantly male and why carrier mothers can pass the condition to their sons. Other inheritance patterns don’t fit this pattern: autosomal recessive would affect both sexes roughly equally and require two mutated copies; autosomal dominant would often appear in every generation and affect both sexes; X-linked dominant would often show affected fathers passing to all daughters.