Clinical and molecular characterization of X-linked hyper-IgM syndrome patients in China

X-linked Hyper-IgM syndrome (XHIM) is caused by mutations of CD154 gene also known as CD40 ligand (CD40L). CD40L is expressed in activated T cells and interacts with CD40 receptor expressed on B lymphocytes and dendritic cells. Affected patients present cellular and humoral immune defects, with infections by intracellular, opportunistic and extracellular pathogens. In the present study, we investigate molecular defects involved in the XHIM in five patients and identified five distinct CD40L mutations, three of which had not been previously described. P1 harboured a novel p.L193P mutation, which abolished the expression of CD40L. P2 had a frameshift deletion in exon 3 (p.E108fsX19), which also decreased the protein expression. P3 demonstrated p.E54X change in exon 2. P4 harboured the p.Q186X change in the exon 5. P5 demonstrated p. E142X change in exon 5. Mutations in P3, P4 and P5 all led to the production of premature CD40L protein. Two of the five genetically defined patients received umbilical cord blood stem cell transplantation from unrelated donor and achieved clinical remission, and the expression of CD40L on the peripheral blood mononuclear cells restored. These mutations reflect the heterogeneity of CD40L gene, indicating the need for accurate and reliable molecular testing in patients suspected of XHIM.