The c.822C>A variant in the glucokinase gene, GCK, is a missense variant resulting in an amino acid change of aspartic acid to glutamic acid at codon 274 (p.(Asp274Glu)) of NM_000162.5. This variant has an incomputable gnomAD v4.1.0 Grpmax filtering allele frequency due to the presence of only 1 copy in any subpopulation, thereby meeting the ClinGen MDEP threshold criteria for PM2_Supporting (Grpmax FAF less than or equal to 0.000003) (PM2_Supporting). 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). Additionally, it is predicted to be deleterious by computational evidence, with a REVEL score of 0.929, which is greater than the MDEP VCEP threshold of 0.70 (PP3). This variant was identified in five unrelated individuals with hyperglycemia (PS4_Moderate; PMIDs: 19790256, 34440516, 36178555; internal lab contributors). Additionally, one of these individuals had 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; PMID: 36178555, internal lab contributors). Another missense variant, c.821A>C p.(Asp274Ala), has been classified as pathogenic by the ClinGen MDEP but has a greater Grantham distance than p.(Asp274Glu) (PM5_Supporting). In summary, c.822C>A variant meets the criteria to be classified as likely pathogenic for monogenic diabetes. ACMG/AMP criteria applied, as specified by the ClinGen MDEP VCEP (specification version 3.0.0, approved 7/23/2025): PM2_Supporting, PM5_Supporting, PP2, PP3, PP4_Moderate, PS4_Moderate.