Medical Genetics C Hyper-IgM immunodeficiency A congenital, usually X-linked immunodeficiency characterized by elevated levels of igm, decreased levels of IgG and Iga, intermittent neutropenia, normal B-cell levels and susceptibility to infectionMedical Genetics C. Hyper-IgM immunodeficiency A congenital, usually X-linked immunodeficiency characterized by elevated levels of IgM, decreased levels of IgG and IgA, intermittent neutropenia, normal B-cell levels, and susceptibility to infection