A 5-Year-Old Boy Has a History of Recurrent Pneumococcal Pneumonia,Pneumocystis

Multiple Choice

A 5-year-old boy has a history of recurrent pneumococcal pneumonia,Pneumocystis carinii pneumonia (PCP) ,and bacterial ear infections.His maternal uncle and an older brother experienced the same symptoms,but he has an older sister who is healthy.Laboratory studies indicate normal numbers of B cells and T cells,and the serum contains mostly IgM and very little IgG.If this patient did have a sister affected with the same condition,which of the following genes would most likely contain a mutation?

A) AID (activation-induced deaminase)
B) CD40
C) CD40L
D) CD28
E) CTLA-4