A healthy couple has a son that is affected with Bruton's ag

Discussion in 'USMLE STEP 1' started by Guest, Mar 3, 2010.

  1. Guest

    Guest Guest

    A healthy couple has a son that is affected with Bruton's agammaglobulinemia. If the couple conceives another son, what is the probability that the son would be affected with Bruton's agammaglobulinemia?

    A. 25%
    B. 50%
    C. 67%
    D. 75%
    E. 100%
  2. Guest

    Guest Guest

    Choice (B) is the answer.
    Bruton's agammaglobulinemia is an X-linked recessive immunodeficiency disease characterized by the absence of mature B-cells, which results in the inability to produce antibodies. Patients present in infancy with recurrent infections, including recurrent otitis media with H. influenza and S. pneumonia. S. aureus is also a common infection. Diarrheal infections with Giardia and Campylobacter organisms are often seen, as well, and are difficult to treat. Bruton's agammaglobulinemia is X-linked recessive, so the mother must be a carrier. Sons receive their X chromosome from their mother. Any son born to this couple has a 50% chance of receiving the mutated X chromosome from the mother, which would result in Bruton's agammaglobulinemia. The father contributes a Y chromosome to male offspring. The other choices are incorrect.

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