Human Germline Heterozygous Gain-of-Function STAT6 Variants Cause Severe Allergic Disease

STAT6 (Signal transducer and activator of transcription 6) is a transcription factor that plays a central role in the pathophysiology of allergic inflammation. STAT6 mediates the biological effects of IL-4, a cytokine necessary for type 2 differentiation of T cells and B cell survival, proliferation and class switching to IgE. We have identificated two unrelated patients with a phenotype notable for their early-life onset of profound allergic immune dysregulation, widespread treatment-resistant atopic dermatitis, hypereosinophilia with esosinophilic esophagitis, elevated serum IgE, IgE-mediated food allergies, and vascular anomalies of the brain. Both patients harbored heterozygous de novo missense variants in the DNA binding domain of STAT6 (c.1144G>C, p.E382Q; and c.1256A>G, p.D419G). Functional studies established that both variants caused a gain-of-function (GOF) phenotype associated with enhanced phosphorylation and transcriptional activity of STAT6, in addition to increased transcript abundance of known STAT6 target genes and other genes implicated in allergic disease. JAK inhibitors decreased the enhanced STAT6 responses associated with both these STAT6 GOF variants. This study identifies heterozygous GOF variants in STAT6 as a novel autosomal dominant allergic disorder. We anticipate that our discovery of the first humans with germline STAT6 GOF variants will facilitate the recognition of more affected individuals and the full definition of this new primary atopic disorder.