Molecular analysis of a large cohort of patients with the hyper immunoglobulin M (IgM) syndrome

The hyper immunoglobulin M (IgM) syndrome (HIGM), characterized by recurrent infections, low serum IgG and IgA, normal or elevated IgM, and defective class switch recombination and somatic hypermutation, is a heterogenous disorder with at least 5 distinct molecular defects, including mutations of the genes coding for the CD40 ligand (CD40L) and IKK-gamma (NEMO) genes, both X-linked; and mutations of CD40, activation-induced cytidine deaminase (AICDA), and uracil-DNA glycosylase (UNG), associated with autosomal recessive HIGM syndromes. To investigate the molecular basis of HIGM, we determined the prevalence of mutations affecting these 5 genes in a cohort of 140 patients (130 males and 10 females). Those patients without a molecular diagnosis were subsequently evaluated for mutations of the following genes: inducible CO-stimulator molecule (ICOS), ICOS ligand (ICOSL), and if male, Bruton tyrosine kinase (Btk) and SLAM-associated protein (SAP/SH2D1A). We found mutations of CD40L in 98 males; AICDA in 4 patients (3 males, 1 female); UNG in one adult male; and Btk in 3 boys. Of the remaining 25 males, one infant with hypohidrotic ectodermal dysplasia had a mutation of NEMO. None of the remaining 33 patients (24 males/9 females) had mutations affecting CD40, ICOS, ICOSL, or SH2D1, and are best classified as common variable immune deficiency (CVID), although other genes, including some not yet identified, may be responsible.