The c.389T>A variant in the glucokinase gene, GCK, causes an amino acid change of isoleucine to asparagine at codon 130 (p.(Ile130Asn)) 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 0.937, 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 2 unrelated individuals with hyperglycemia; however, PS4_Moderate cannot be applied because this number is below the ClinGen MDEP threshold (internal lab contributors). This variant segregated with hyperglycemia, with 4 informative meioses in 2 families (PP1_Strong; internal lab contributors). Another missense variant, c.389T>C p.Ile130Thr, has been classified as likely pathogenic by the ClinGen MDEP (PM5_Supporting). In summary, c.389T>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): PP2, PP3, PM2_Supporting, PM5_Supporting, PP1_Strong.