CD79A and immune system disorder: Such mutations manifest as combined immunodeficiencies of varying severity, such as leaky SCID.44 One such case was recently described in a patient with a disease mimicking hyper‐IgM syndrome with high serum IgM and low IgG and IgA levels, lymphocytosis and recurrent infections, intractable diarrhoea, growth retardation, systemic cytomegalovirus infection and sclerosing cholangitis.