The c.437T>G variant in the glucokinase gene, GCK causes an amino acid change of leucine to arginine at codon 210 (p.(Leu146Arg)) 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 also predicted to be deleterious by computational evidence, with a REVEL score of 0.981, 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 an individual with a clinical history highly specific for GCK-hyperglycemia (FBG 5.5-8 mmol/L and HbA1c 5.6 - 7.6%) (PP4; PMIDs: 24804978, 29927023). A kinetic analysis of recombinant wild-type (WT) and mutant glucokinase demonstrated that the wild-type kinetic parameters pass the quality control, the wild-type ATP Km is between 0.4-0.65, and the p.Leu146Arg variant has a relative activity index (RAI) <0.50 (PS3_Moderate; PMID: 16731834). Another missense variant, c.437T>C p.Leu146Pro, has been interpreted as pathogenic by the ClinGen MDEP VCEP and p.Leu146Arg has a greater Grantham distance. (PM5). This variant was identified in three unrelated individuals with a clinical picture consistent with monogenic diabetes; however, PS4_Moderate cannot be applied because this number is below the MDEP threshold (PMID 18399931, 24804978, 29927023, internal lab contributors). In summary, this 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 1.3.0, approved 8/13/2023): PS3_Moderate, PP2, PM2_Supporting, PP3, PP4, PM5.