Dysgammaglobulinemia Associated With Glu349del, a Hypomorphic XIAP Mutation.
Hyper-IgM syndromes (HIGM) are characterized by low levels of IgG, IgA and IgE and normal to high levels of IgM. Patients with these syndromes present recurrent infections due to an impaired immunoglobulin maturation. The most prevalent form of HIGM, X-linked hyper IgM syndrome (XHIM), is caused by mutations in the gene encoding the CD40 ligand (CD40LG). We present two siblings with XHIM caused by a large CD40LG deletion affecting more than half of the gene, and extended from the end of intron 3 to far upstream of the promoter regions. Genetic analysis in the maternal family discovered the CD40L(G219R) polymorphism in several members. Segregation of this polymorphism in the kindred indicated that the deletion of CD40LG was a de novo mutation in the mother. Although half of her CD4+ T cells did not express CD40L and the other half expressed the CD40L(G219R) variant, the mother was healthy. This suggests that this polymorphism is not pathogenic by itself although it has been recently related to X-linked lymphoproliferative syndrome.