The c.605C>T variant in the glucokinase gene, GCK, causes an amino acid change of methionine to threonine at codon 202 (p.(Met202Thr)) of NM_000162.5. This variant segregated with diabetes/hyperglycemia, with 6 informative meioses in 4 families (PP1_Strong; internal lab contributors). This variant was identified in 12 unrelated individuals with hyperglycemia (PS4; PMID: 17573000, internal lab contributors). This variant was identified in two individuals 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). 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 0.917, which is greater than the MDEP VCEP threshold of 0.70 (PP3). This variant has a gnomAD v2.1.1 Popmax filtering allele frequency of 0.000002920 (below the MDEP threshold of 0.000003) and 2 copies observed in the European non-Finnish population and 0 copies in any other subpopulation, thereby meeting the ClinGen MDEP criteria for PM2_Supporting (PM2_Supporting). In summary, c.605C>T meets the criteria to be classified as pathogenic for monogenic diabetes. ACMG/AMP criteria applied, as specified by the ClinGen MDEP (specification version 1.3.0, approved 8/11/2023): PP1_Strong, PS4, PP4_Moderate, PP2, PP3, PM2_Supporting.