The c.1322C>G variant in the glucokinase gene, GCK, causes an amino acid change of glycine to asparagine at codon 441 (p.(Ser441Trp)) of NM_000162.5. This variant is absent from gnomAD v2.1.1 (PM2_Supporting). 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 0.967, which is greater than the MDEP VCEP threshold of 0.70 (PP3). This variant was identified in an individual with a clinical history highly specific for GCK-MODY (FBG 5.5-8 mmol/L and HbA1c 5.6 - 7.6% and OGTT increment < 3.0 mmol/L) (PP4_Moderate; PMID: 25665835). 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.Ser441Trp has RAI=0.11, which is less than the MDEP VCEP threshold of 0.50 (PS3_Moderate; PMID 19884385). This variant was identified in 8 unrelated individuals with non-autoimmune and non-absolute/near-absolute insulin-deficient diabetes (PS4; PMID: 27420379, 25665835, 19884385, 17573900, 16965331, 11508276, internal lab contributors). In summary, 1322C>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 1.2.0, approved 6/7/2023): PM2_Supporting, PP2, PP3, PP4_Moderate, PS3, PS4.