Hyper-IgM syndrome type 2 (HIGM2) is characterized by normal or elevated serum IgM levels with absence of IgG, IgA, and IgE, resulting in a profound susceptibility to bacterial infections. There is an absence of immunoglobulin class switch recombination (CSR), a lack of immunoglobulin somatic hypermutations, and lymph node hyperplasia caused by the presence of giant germinal centers. This is an autosomal recessive disorder responsible for approximately 30% of Ig deficiencies with increased IgM.