The c.410A>G variant in the glucokinase gene, GCK, causes an amino acid change of histidine to arginine at codon 137 (p.(His137Arg)) 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). The variant is absent in gnomAD v2.1 and v4.1 (PM2_Supporting). It has a REVEL score of 0.598, which is between the ClinGen MDEP thresholds for BP4 and PP3, predicting neither a damaging nor benign impact on GCK function. While studies exploring the effect of this variant on protein function have been performed, these studies do not meet the criteria set forth by the MDEP for the application of PS3 or BS3 (PMID: 10525657, 14517946). This variant was identified in two unrelated cases with hyperglycemia; however, PS4_Moderate cannot be applied because this number is below the ClinGen MDEP threshold (PMID: 904948, internal lab contributors). 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; internal lab contributor). Additionally, this variant segregated with hyperglycemia, with nine informative meioses in a single family (PP1_Strong; PMID: 9049484). In summary, c.410A>G meets the criteria to be classified as a likely pathogenic for monogenic diabetes. ACMG/AMP criteria applied, as specified by the ClinGen MDEP (specification version 2.0.0, approved 8/11/2023): PP1_Strong, PP4_Moderate, PM2_Supporting, PP2.