X-linked hyper IgM syndrome is a condition that affects the immune system and occurs almost exclusively in males. People with this disorder have abnormal levels of proteins called antibodies or immunoglobulins. Antibodies help protect the body against infection by attaching to specific foreign particles and germs, marking them for destruction. There are several classes of antibodies, and each one has a different function in the immune system. Although the name of this condition implies that affected individuals always have high levels of immunoglobulin M (IgM), some people have normal levels of this antibody. People with X-linked hyper IgM syndrome have low levels of three other classes of antibodies: immunoglobulin G (IgG), immunoglobulin A (IgA), and immunoglobulin E (IgE). The lack of certain antibody classes makes it difficult for people with this disorder to fight off infections.

Individuals with X-linked hyper IgM syndrome begin to develop frequent infections in infancy and early childhood. Common infections include pneumonia, sinus infections (sinusitis), and ear infections (otitis). Infections often cause these children to have chronic diarrhea and they fail to gain weight and grow at the expected rate (failure to thrive). Some people with X-linked hyper IgM syndrome have low levels of white blood cells called neutrophils (neutropenia). Affected individuals may develop autoimmune disorders, neurologic complications from brain and spinal cord (central nervous system) infections, liver disease, and gastrointestinal tumors. They also have an increased risk of lymphoma, which is a cancer of immune system cells.

The severity of X-linked hyper IgM syndrome varies among affected individuals, even among members of the same family. Without treatment, this condition can result in death during childhood or adolescence.

X-linked hyper IgM syndrome is estimated to occur in 2 per million newborn boys.

Variants (also known as mutations) in the CD40LG gene cause X-linked hyper IgM syndrome. This gene provides instructions for making a protein called CD40 ligand, which is found on the surface of immune system cells known as T cells. CD40 ligand attaches like a key in a lock to its receptor protein, which is located on the surface of immune system cells called B cells. B cells are involved in the production of antibodies, and initially they are able to make only IgM antibodies. When CD40 ligand and its receptor protein are connected, they trigger a series of chemical signals that instruct the B cell to start making IgG, IgA, or IgE antibodies.

CD40 ligand is also necessary for T cells to interact with other cells of the immune system, and it plays a key role in the maturation (differentiation) of T cells, which allows them to carry out their specific functions. 

Variants in the CD40LG gene lead to the production of an abnormal CD40 ligand or prevent production of this protein. If CD40 ligand does not attach to its receptor on B cells, these cells cannot produce IgG, IgA, or IgE antibodies. Variants in the CD40LG gene also impair the T cell's ability to mature and interact with other immune system cells. People with X-linked hyper IgM syndrome are prone to infections because they do not have a properly functioning immune system.

Genetic Testing Information

• Genetic Testing Registry: Hyper-IgM syndrome type 1

Genetic and Rare Diseases Information Center

• X-linked hyper-IgM syndrome

Patient Support and Advocacy Resources

• National Organization for Rare Disorders (NORD)

Clinical Trials

• ClinicalTrials.gov

Catalog of Genes and Diseases from OMIM

• IMMUNODEFICIENCY WITH HYPER-IgM, TYPE 1; HIGM1

Scientific Articles on PubMed

• PubMed

• Bhushan A, Covey LR. CD40:CD40L interactions in X-linked and non-X-linked hyper-IgM syndromes. Immunol Res. 2001;24(3):311-24. doi: 10.1385/IR:24:3:311. Citation on PubMed
• Dunn CP, de la Morena MT. X-Linked Hyper IgM Syndrome. 2007 May 31 [updated 2020 Feb 20]. In: Adam MP, Feldman J, Mirzaa GM, Pagon RA, Wallace SE, Amemiya A, editors. GeneReviews(R) [Internet]. Seattle (WA): University of Washington, Seattle; 1993-2024. Available from http://www.ncbi.nlm.nih.gov/books/NBK1402/ Citation on PubMed
• Durandy A. Hyper-IgM syndromes: a model for studying the regulation of class switch recombination and somatic hypermutation generation. Biochem Soc Trans. 2002 Aug;30(4):815-8. doi: 10.1042/bst0300815. Citation on PubMed
• Gilmour KC, Walshe D, Heath S, Monaghan G, Loughlin S, Lester T, Norbury G, Cale CM. Immunological and genetic analysis of 65 patients with a clinical suspicion of X linked hyper-IgM. Mol Pathol. 2003 Oct;56(5):256-62. doi: 10.1136/mp.56.5.256. Citation on PubMed or Free article on PubMed Central
• Jain A, Atkinson TP, Lipsky PE, Slater JE, Nelson DL, Strober W. Defects of T-cell effector function and post-thymic maturation in X-linked hyper-IgM syndrome. J Clin Invest. 1999 Apr;103(8):1151-8. doi: 10.1172/JCI5891. Citation on PubMed or Free article on PubMed Central
• Levy J, Espanol-Boren T, Thomas C, Fischer A, Tovo P, Bordigoni P, Resnick I, Fasth A, Baer M, Gomez L, Sanders EA, Tabone MD, Plantaz D, Etzioni A, Monafo V, Abinun M, Hammarstrom L, Abrahamsen T, Jones A, Finn A, Klemola T, DeVries E, Sanal O, Peitsch MC, Notarangelo LD. Clinical spectrum of X-linked hyper-IgM syndrome. J Pediatr. 1997 Jul;131(1 Pt 1):47-54. doi: 10.1016/s0022-3476(97)70123-9. Citation on PubMed
• Thusberg J, Vihinen M. The structural basis of hyper IgM deficiency - CD40L mutations. Protein Eng Des Sel. 2007 Mar;20(3):133-41. doi: 10.1093/protein/gzm004. Epub 2007 Feb 16. Citation on PubMed
• Winkelstein JA, Marino MC, Ochs H, Fuleihan R, Scholl PR, Geha R, Stiehm ER, Conley ME. The X-linked hyper-IgM syndrome: clinical and immunologic features of 79 patients. Medicine (Baltimore). 2003 Nov;82(6):373-84. doi: 10.1097/01.md.0000100046.06009.b0. Citation on PubMed