The c.162T>G variant in the glucokinase gene, GCK, causes an amino acid change of serine to arginine at codon 54 (p.(Ser54Arg)) 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 0.713, which is greater than the MDEP VCEP threshold of 0.70 (PP3). This variant has an incomputable gnomAD v2.1.1 Grpmax filtering allele frequency due to zero copies present in the European non-Finnish subpopulation and any other non-Founder subpopulation, thereby meeting the ClinGen MDEP threshold criteria for PM2_Supporting. There are three copies present in the European Finnish population; however, given that this is a Founder sub-population, PM2_Supporting will still be applied (PM2_Supporting). This variant was identified in at least 4 unrelated individuals with non-autoimmune and non-absolute/near-absolute insulin-deficient diabetes; however PS4_Moderate will not be applied at this time given that all cases were identified in the Finnish population (internal lab contributors). At least 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 contributors). Additionally, this variant segregated with diabetes, with at least 4 informative meioses in multiple families (PP1_Strong; internal lab contributors). In summary, c.162T>G meets the criteria to be classified as likely pathogenic for monogenic diabetes. ACMG/AMP criteria applied, as specified by the ClinGen MDEP (specification version 1.3.0, approved 8/11/2023): PP2, PP3, PM2_Supporting, PP4_Moderate, PP1_Strong.