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?

Question

Quizplus · Accepted Answer

If the patient's sister is also affected with hyper-IgM syndrome,then the inheritance pattern is autosomal recessive.Both the AID and CD40 genes are located on autosomal chromosomes,and mutations in both have been identified as causes of hyper-IgM syndrome.However,only a mutation in CD40 will result in reduced macrophage function and susceptibility to Pneumocystis carinii pneumonia,as is observed in this patient.

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