The c.1132G>A variant in the glucokinase gene, GCK, causes an amino acid change of alanine to threonine at codon 378 (p.(Ala378Thr) of NM_000162.5. This variant failed quality control check in gnomAD 2.1.1; however, it is absent in multiple large population cohorts (UKBiobank, BioMe, Geisinger, internal lab contributors) and therefore the ClinGen MDEP has approved the application of PM2_Supporting for this variant (PM2_Supporting). This variant is predicted to be deleterious by computational evidence, with a REVEL score of 0.921, which is greater than the MDEP VCEP threshold of 0.70 (PP3). Another missense variant, c.1133C>T (p.(Ala378Val)), has been classified as pathogenic by the ClinGen MDEP VCEP but has a greater Grantham distance than p.Ala378Thr (PM5_Supporting). Additionally, GCK is defined by the ClinGen MDEP VCEP as a gene that has a low rate of benign missense variation and where pathogenic missense variants are a common mechanism of disease (PP2). This variant has been identified in over 30 unrelated individuals with non-autoimmune/insulin-dependent diabetes (PS4; PMID 18248649, PMID 16965331, internal lab contributors). This variant segregates with diabetes in 15 informative meioses in a large extended family with diabetes (PP1_Strong; internal lab contributor). This variant was identified in an individual with a clinical history highly specific for GCK-hyperglycemia (FBG 5.5-8 mmol/L and HbA1c 5.6 - 7.6% and negative antibodies) (PP4_Moderate; internal lab contributors). In summary, c.1132G>A meets the criteria to be classified as pathogenic for monogenic diabetes. ACMG/AMP criteria applied, as specified by the ClinGen MDEP (specification version 1.2.0, approved 6/7/2023): PM2_Supporting, PP3, PM5_Supporting, PP2, PS4, PP1_Strong, PP4_moderate.