The minor spliceosome is a master immune regulator

Pathogenic variants in non-coding genes are emerging as critical contributors to human rare diseases. We identified 19 individuals with early-onset diabetes (diagnosed <5 years) and additional clinical features who had biallelic pathogenic variants in the novel disease gene RNU6ATAC (n=7) or in RNU4ATAC (n=12). Both genes encode non-coding components of the minor spliceosome, a protein-RNA complex mediating splicing of [~]700 genes containing U12/minor-type introns. RNA-seq of whole blood from six patients showed aberrant splicing of minor intron-containing genes in individuals with RNU6ATAC (n=3) or RNU4ATAC (n=3) variants. 50% of patients tested were islet-autoantibody positive, and 12/19 had additional immune features of immune dysregulation. Analysis of patients transcriptomic, methylation and immune data revealed impaired B cell development and maturation. Biallelic disease-causing variants in RNU6ATAC and RNU4ATAC therefore cause syndromic early-onset autoimmune diabetes and immune dysregulation, highlighting the critical role of the minor spliceosome as a master regulator of the human immune system.