The c.1318G>T variant in the glucokinase gene, GCK, results in a premature termination at codon 440 (p.(Glu440Ter)) of NM_000162.5. While this variant, located in exon 10 of 10, is predicted to cause a premature stop codon and to escape nonsense mediated decay, it is in a functionally important region of a gene where loss-of-function is an established disease mechanism (PVS1). This variant is absent in gnomAD (PM2_Supporting). This variant was identified in at least two individuals with a clinical history highly specific for GCK-MODY (FBG 5.5-8 mmol/L and HbA1c 5.6 - 7.6% and negative antibodies) (PP4_Moderate; internal lab contributors). This variant was identified in 7 unrelated individuals with non-autoimmune and non-absolute/near-absolute insulin-deficient diabetes (PS4; PMIDs: 23890519, 25041077, DOI: 10.1530/endoabs.35.P371, and internal lab contributors). This variant segregated with diabetes, with 4 informative meioses in 4 families with MODY (PP1_Strong; PMID: 25041077, DOI: 10.1530/endoabs.35.P371, internal lab contributors). In summary, the c.1318G>T variant meets the criteria to be classified as pathogenic for monogenic diabetes. ACMG/AMP criteria applied, as specified by the ClinGen MDEP (specification version 1.2.0, approved 6/7/2023): PVS1, PM2_Supporting, PP4_Moderate, PS4, PP1_Strong.