The c.1112G>T variant in the glucokinase gene, GCK, causes an amino acid change of cysteine to phenylalanine at codon 371 (p.(Cys371Phe)) of NM_000162.5. GCK is defined by the ClinGen MDEP VCEP as a gene that has a low rate of benign missense variation and where pathogenic missense variants are a common mechanism of disease (PP2). This variant is predicted to be deleterious by computational evidence, with a REVEL score of 0.931, 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 hyperglycemia (PS4; PMID 24735133, internal lab contributors). This variant segregated with hyperglycemia with 12 informative meioses in 3 families with MODY (PP1_Strong; internal lab contributors). This variant was identified in at least two individuals with a clinical history highly specific for GCK-hyperglycemia (FBG 5.5-8 mmol/L and HbA1c 5.6 - 7.6% as well as either OGTT increment < 3 mmol/L or negative antibodies) (PP4_Moderate; internal lab contributors). In summary, this variant meets the criteria to be classified as pathogenic for monogenic diabetes. ACMG/AMP criteria applied, as specified by the ClinGen MDEP VCEP (specification version 1.2.0, approved 6/7/2023) : PP2, PP3, PM2_Supporting, PP1_Strong, PS4, PP4_Moderate .