The c.1148C>G variant in the glucokinase gene, GCK, causes an amino acid change of serine to tryptophan at codon 383 (p. (Ser383Trp)) 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 located in the larger hexokinase domain of the GCK gene (PMID: 31638168) but this variant does not reside in an amino acid that directly binds glucose or ATP, which is defined as critical for the protein’s function by the ClinGen MDEP, so it does not meet PM1. This variant is predicted to be deleterious by computational evidence, with a REVEL score of 0.85 which is greater than the MDEP VCEP threshold of 0.70 (PP3). Another missense variant, c.1148C>T (p.Ser383Leu), has been interpreted as pathogenic by the ClinGen MDEP, and p.Ser383Trp has an equal or greater Grantham distance (PM5). This variant was found in one family, and segregated with hyperglycemia, with four informative meioses (PP1_Moderate; PMID: 3385223). In summary, c.1148C>G meets the criteria to be classified as likely pathogenic for monogenic diabetes. ACMG/AMP criteria applied, as specified by the ClinGen MDEP VCEP (VCEP specifications version v1.3.0; approved 8/11/2023): PP3, PP2, PP1_Moderate, PM5, PM2_Supporting