A rare genetic non-severe combined immunodeficiency disorder with characteristics of normal or elevated IgM serum levels with low or absent IgG, IgA and IgE serum concentrations, which manifests with recurrent or severe bacterial infections and increased susceptibility to opportunistic infections (in particular, pneumonia due to P. jiroveci, but also chronic cryptosporidial, cryptococcal, cytomegalovirus and toxoplasma infections). Haematologic disorders (neutropenia, anaemia, thrombocytopenia) are frequently associated. Immunologic findings reveal decreased numbers of CD27+ memory B cells and lack of germinal centre formation. [from
SNOMEDCT_US]