The c.749G>A variant in the glucokinase gene, GCK, causes an amino acid change of arginine to histidine at codon 250 (p.(Arg250His)) of NM_000162.5. This variant was identified in an individual with a clinical history highly specific for GCK-hyperglycemia (pediatric patient with incidental diagnosis with FBG 5.5-8 mmol/L and HbA1c 5.6 - 7.6% persistently and negative antibodies (PP4_Moderate; PMID: 28170077, internal lab contributors). 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). 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 has an incomputable gnomAD v2.1.1 Popmax minor filtering allele frequency due to 0 copies in the European non-Finnish subpopulation and 1 copy in the African/African American subpopulation, thereby meeting the ClinGen MDEP threshold criteria for PM2_Supporting (ENF Popmax FAF <= 0.000003 and <= 2 copies in ENF and <=1 copy in any other subpopulation) (PM2_Supporting). Another missense variant, c.748C>T p.Arg250Cys, has been classified as pathogenic by the ClinGen MDEP but has a greater Grantham distance than p.Arg250His (PM5_Supporting). The relative activity index (RAI) of this variant was above the MDEP cutoff of 0.5, and thermostability was not evaluated, and neither PS3 nor BS3 could be applied (PMID: 30592380). In summary, c.749G>A 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, PP2, PP3, PM2_Supporting, PM5_Supporting.