The c.1136C>A variant in the glucokinase gene, GCK, causes an amino acid change of alanine to proline at codon 379 (p.(Ala379Glu)) 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 0.985, 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 five unrelated individuals with non-autoimmune/insulin-deficient diabetes (PS4_Moderate; PMID 30592380, internal lab contributors). This variant was identified in an individual with a clinical history highly specific for GCK-MODY (FBG 5.5-8 mmol/L and HbA1c 5.6 - 7.6%) (PP4; PMID: 30592389) (PP4; internal lab contributors). This variant has been detected in one individual with neonatal diabetes. This individual was compound heterozygous for the variant and a pathogenic variant and was confirmed in trans by parental/family testing (PM3; PMID 30592380). Functional studies demonstrated the p.Ala379Glu protein has RAI<0.5; however, the wild-type kinetic parameters didn’t pass the quality control, and the PS3 cannot be applied (PMID: 30592380). In summary, this variant meets the criteria to be classified as likely 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, PP4, PM3, PS4_Moderate.