The c.682A>G variant in the glucokinase gene, GCK, causes an amino acid change of threonine to alanine at codon 228 (p.(Thr228Ala)) of NM_000162.5. GCK is defined by the ClinGen MDEP as a gene that has a low rate of benign missense variation and has pathogenic missense variants as a common mechanism of disease (PP2). This variant is predicted to be deleterious by computational evidence, with a REVEL score of 0.931 which is greater than the MDEP VCEP threshold of 0.70 (PP3). This variant resides in an amino acid that directly binds ATP, which is defined as critical for the protein’s function by the ClinGen MDEP (PM1). This variant has an incomputable gnomAD v2.1.1 Grpmax filtering allele frequency due to 1 copy in the East Asian subpopulation and no copies in any other subpopulation, thereby meeting the ClinGen MDEP threshold criteria for PM2_Supporting (ENF Popmax FAF <= 0.000003 and <= 2 copies in ENF and <=1 copy in any other subpopulation) (PM2_Supporting). This variant was identified in 7 unrelated individuals with hyperglycemia (PS4, PMIDs: 31638168, 12955723, internal lab contributors). Another missense variant, c.683C>T p.Thr228Met, has been classified as pathogenic by the ClinGen MDEP but has a greater Grantham distance than p.Thr228Ala (PM5_Supporting). In summary, c.682A>G meets the criteria to be classified as pathogenic for monogenic diabetes. ACMG/AMP criteria applied, as specified by the ClinGen MDEP (specification version 1.3, approved 8/11/2023): PM1, PP2, PP3, PM2_Supporting, PM5_Supporting, PS4.