Dominant gain-of-function STAT1 mutations in FOXP3 wild-type immune dysregulation–polyendocrinopathy–enteropathy–X-linked–like syndrome

Background Mutations in signal transducer and activator of transcription (STAT) 1 cause a broad spectrum of disease, ranging from severe viral and bacterial infections (amorphic alleles) to mild disseminated mycobacterial disease (hypomorphic alleles) to chronic mucocutaneous candidiasis (CMC; hypermorphic alleles). The hypermorphic mutations are also associated with arterial aneurysms, autoimmunity, and squamous cell cancers. Objective We sought to investigate the role of STAT1 gain-of-function mutations in phenotypes other than CMC. Methods We initially screened patients with CMC and autoimmunity for STAT1 mutations. We functionally characterized mutations in vitro and studied immune profiles and regulatory T (Treg) cells. After our initial case identifications, we explored 2 large cohorts of patients with wild-type forkhead box protein 3 and an immune dysregulation–polyendocrinopathy–enteropathy–X-linked (IPEX)–like phenotype for STAT1 mutations. Results We identified 5 children with polyendocrinopathy, enteropathy, and dermatitis reminiscent of IPEX syndrome; all but 1 had a variety of mucosal and disseminated fungal infections. All patients lacked forkhead box protein 3 mutations but had uniallelic STAT1 mutations (c.629 G>T, p.R210I; c.1073 T>G, p.L358W, c.796G>A; p.V266I; c.1154C>T, T385M [2 patients]). STAT1 phosphorylation in response to IFN-γ, IL-6, and IL-21 was increased and prolonged. CD4+ IL-17–producing T-cell numbers were diminished. All patients had normal Treg cell percentages in the CD4+ T-cell compartment, and their function was intact in the 2 patients tested. Patients with cells available for study had normal levels of IL-2–induced STAT5 phosphorylation. Conclusions Gain-of-function mutations in STAT1 can cause an IPEX-like phenotype with normal frequency and function of Treg cells.