This decrease in the percentage of switched memory B cells reflects the hypogammaglobulinemia and selective IgG antibody deficiency found in the patient and could also be responsible for the observed impairment in IgG production by patient A ́s EBV-transformed B cells, although an additional effect of the patient ́s RAG1 deficiency on immunoglobulin class switching cannot be ruled out.[42] Expansion of CD21low B cells is predominately found in HIV infected individuals and in a specific subgroup of CVID patients[43,44]. This evidence concerns the gene RAG1 and hyperinsulinemic hypoglycemia, familial, 4.