Immunodeficiency with Hyper-IgM, X-Linked, Type 1

**Semantic type:** Disease or Syndrome

**Definition:** An X-linked subtype of hyper-IgM caused by mutation(s) in the CD40LG gene, encoding CD40 ligand. It is characterized by normal or elevated IgM concentrations, with markedly decreased concentrations of other immunoglobulins. The clinical course is variable; it manifests as susceptibility to bacterial and opportunistic infections, neutropenia, and increased risk of lymphoma.

**Synonyms:** - HIGM1 - Hyper-IgM Syndrome 1 - X-Linked Hyper-IgM Syndrome