 These three patients instead had mutations in the catalytic domain of uracil-DNA glycosylase, an enzyme that removes uracil from DNA.In hyper-IgM syndromes, patients are deficient in the immunoglobulins, IgG, IgE and IgA types since the antibody producing B cells can not carry out the gene recombination steps necessary to class switch from immunoglobulin M (IgM) to the other three immunoglobulins types.Hyper IgM syndromes is a group of primary immune deficiency disorders characterized by defective CD40 signaling; "via" B cells affecting class switch recombination (CSR) and somatic hypermutation.