The c.1322C>T variant in the glucokinase gene, GCK, causes an amino acid change of glycine to asparagine at codon 441 (p.(Ser441Leu)) of NM_000162.5. This variant has a non-calculable Popmax filtering allele frequency, with absence in the gnomAD v2.1.1 European non-Finnish population and one copy in the African/African American subpopulation, which is less than the ClinGen MDEP threshold for PM2_Supporting (ENF Popmax FAF <= 0.000003 and <= 2 copies in ENF and <=1 copy in any other subpopulation) (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). The variant is predicted to be deleterious by computational evidence, with a REVEL score of 0.984, 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%) (PP4; PMID: 28726111). Another missense variant, c.1322C>G p.(Ser441Trp), has been classified as pathogenic by the ClinGen MDEP but has a greater Grantham distance than p.(Ser441Leu) (PM5_Supporting). In summary, c.1322C>T meets the criteria to be classified as uncertain significance for monogenic diabetes. ACMG/AMP criteria applied, as specified by the ClinGen MDEP (specification version 1.2.0, approved 6/7/2023): PM2_Supporting, PP3, PP2, PP4, PM5_Supporting.