Epigenetic signature at FOXP3 distal enhancer affects regulatory T cell development in Kabuki syndrome

Kabuki syndrome (KS) is a congenital developmental disorder caused by germinal pathogenic variants in the lysine methyltransferase 2D (KMT2D, KS1) or lysine demethylase 6A (KDM6A, KS2) genes. Kabuki patients display mental retardation, multiorgan malformations and immune dysregulation - ranging from immunodeficiency to autoimmunity - which strongly compromises their life expectancy. We explored whether the complex immunological scenario of Kabuki syndrome 1 subjects (Ks) could be ascribed to an altered generation of CD4+FOXP3+ regulatory T cells (Tregs). We report that pediatric Ks carrying KMT2D pathogenic variants show a significant reduction of Tregs. DNA methylation analysis reveals a specific methylation pattern at the FOXP3 distal enhancer that correlates with decreased FOXP3 transcription early during Treg cell induction and promotes T helper (Th)-2 lineage differentiation. Finally, in vitro T cell demethylation rescues FOXP3 expression and Treg induction in Ks, offering a novel potential therapeutic perspective. Our findings connect KMT2D loss-of-function to the inhibition of human FOXP3 gene transcription and provide novel molecular insights to explain the immunological phenotype in Ks, thus pinpointing this syndrome as a novel Tregopathy.