Exploiting O-GlcNAc dyshomeostasis to screen O-GlcNAc transferase intellectual disability variants

O-GlcNAcylation is an essential protein modification catalysed by O-GlcNAc transferase (OGT). Missensevariants in OGT are linked to a novel intellectual disability syndrome known as OGT Congenital Disorder ofGlycosylation (OGT-CDG). The mechanisms by which OGT missense variants lead to this heterogeneoussyndrome are not understood, and no unified method exists for dissecting pathogenic from non-pathogenicvariants. Here, we develop a double fluorescence strategy in mouse embryonic stem cells to measuredisruption of O-GlcNAc homeostasis by quantifying the effects of variants on endogenous OGT expression.OGT-CDG variants generally elicited a lower feedback response than wild type and Genome AggregationDatabase (GNOMAD) OGT variants. This approach was then used to dissect new putative OGT-CDGvariants from pathogenic background variants in other disease-associated genes. Our work enables theprediction of pathogenicity for rapidly emerging de novo OGT-CDG variants and points to reduced disruptionof O-GlcNAc homeostasis as a common mechanism underpinning OGT-CDG.