The c.737G>C variant in the glucokinase gene, GCK, causes an amino acid change of glycine to alanine at codon 246 (p.(Gly246Ala)) 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 0.839, which is greater than the MDEP VCEP threshold of 0.70 (PP3). This variant is absent from gnomAD v2.1.1 (PM2_Supporting). This variant was identified in 4 unrelated individuals with hyperglycemia (PS4_Moderate; PMID:27256595, 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 OGTT increment < 3 mmol/L) (PP4_Moderate, PMID:27256595). This variant segregated with hyperglycemia, with 3 informative meioses in 2 families (PP1_Moderate; internal lab contributors). Another missense variant, c.736G>A p.Gly246Arg, has been classified as pathogenic by the ClinGen MDEP but has a greater Grantham distance than p.Gly246Ala (PM5_Supporting). In summary, c.737G>C 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): PP4_Moderate, PS4_Moderate, PP1_Moderate, PP2, PP3, PM2_Supporting, PM5_Supporting.