The c.1181G>T variant in the glucokinase gene, GCK, causes an amino acid change of arginine to leucine at codon 394 (p.(Arg394Leu)) of transcript NM_000162.5. This variant is absent from gnomAD v4.1 (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 0.925 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 three generation family history of diabetes/hyperglycemia) (PP4_Moderate; internal lab contributors). While the relative activity index (RAI) of this variant was above the MDEP cutoff of 0.5, the relative stability index was below the MDEP cutoff of 0.5 (PS3_Supporting; internal lab contributors). Another missense variant at the same amino acid position, c.1181G>C p.Arg394Pro has been classified as likely pathogenic by the ClinGen MDEP (PM5_Supporting). In summary, c.1181G>T meets the criteria to be classified as likely pathogenic for monogenic diabetes. ACMG/AMP criteria applied, as specified by the ClinGen MDEP (specification version 2.0.0, approved 2/17/2025): PM2_Supporting, PP2, PP3, PP4_Moderate, PS3_Supporting, PM5_Supporting.