The c.350G>T variant in the glucokinase gene, GCK, causes an amino acid change of glycine to valine at codon 117 (p.(Gly117Val)) 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 predicted to be deleterious by computational evidence, with a REVEL score of 0.953, 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 two unrelated individuals with hyperglycemia; however, PS4_Moderate cannot be applied because this number is below the ClinGen MDEP threshold (internal lab contributors). One of these individuals had a clinical history highly specific for GCK-hyperglycemia (FBG 5.5-8 mmol/L and HbA1c 5.6 - 7.6% and 2 hour OGTT increment < 3 mmol/L and negative antibodies) (PP4_Moderate; internal lab contributors), identified as a de novo occurrence with unconfirmed parental relationships (PS2_Moderate, Internal lab contributors). In summary, c.350G>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 1.3, approved 8/11/2023): PP4_Moderate, PS2_Moderate, PP2, PP3, PM2_Supporting.