The c.234C>G variant in the glucokinase gene, GCK, causes an amino acid change of aspartic acid to glutamic acid at codon 78 (p.(Asp78Glu)) 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 0.90, which is greater than the MDEP VCEP threshold of 0.70 (PP3). Furthermore, this variant resides in an amino acid that directly binds ATP, which is defined as critical for the protein’s function by the ClinGen MDEP (PM1). This variant was identified in seven unrelated individuals with hyperglycemia (PS4; PMID: 17573900, 30663027, 36504295, 14517956, internal lab contributors). Furthermore, one of these reported individuals had a clinical history highly specific for GCK-hyperglycemia (fasting glucose 5.5-8 mmol/L and HbA1c 5.6 - 7.6% and negative autoantibodies) (PP4_Moderate; PMID: 22060211). Additonally, this variant segregated with hyperglycemia, with 4 informative meioses in three families with hyperglycemia (PP1_Strong; internal lab contributors). In summary, c.234C>G meets the criteria to be classified as pathogenic for monogenic diabetes. ACMG/AMP criteria applied, as specified by the ClinGen MDEP (specification version 1.3.0, approved 8/11/2023): PM2_Supporting, PP2, PP3, PM1, PS4, PP4_Moderate, PP1_Strong).