RESUMEN
X-linked hyper IgM (XHIM) syndrome is a rare congenital immunodeficiency disease caused by failure of B cell to isotype switch from IgM to other classes of immunoglobulins in response to infections. Recently, a molecular cloning of the gene responsible for the syndrome, the CD40L gene has been accomplished and the gene was successfully mapped to the long arm of X chromosome at the position Xq26. We, herein, report the first case of molecular proven XHIM in a Thai boy with a classic presentation and with a confirmed mutation of the CD40L gene. Case Report: A.S. was a 1 year 7 month old boy referred from Buriram Provincial Hospital for a work up and treatment for his recurrent infections consisted of chronic respiratory tract infections with otitis media (since 6 months of age), chronic diarrhea (since 9 months of age) and malnutrition (marasmus) secondary to his longstanding illnesses. He was a product of a consanguineous marriage but without history of similar illness observed in his pedigree. Abnormal laboratory works up included IgG of 300 mg/dl, IgA 10 mg/dl, IgM 1,635 mg/dl, positive stool examinations for Cryptosporidium, chronic colitis on radiographic gastrointestinal follow through study, a positive acid fast bacillus (AFB) stain of gastric aspirate and multiple positive bacterial cultures from various body sources. His anti-HIV serology was negative. His hospital course was significant for several bouts of infections of gastrointestinal, respiratory, and genitourinary systems. His treatment consisted of multiple courses of antibiotics, antituberculous drugs and IVIG administrations. His hospital course was complicated with feeding problem from an esophageal stricture requiring several esophageal dilatations. The analysis of CD40L gene revealed a point mutation of exon 5 (A619T) of the CD40L gene resulting in a stop codon confirming that indeed he had XHIM. He died with Pseudomonas septicemia during the waiting period for a bone marrow transplantation from a cord-blood stem cell.