The c.1348del variant in the glucokinase gene, GCK, causes a frameshift in the protein at codon 450 (NM_000162.5), adding 164 novel amino acids before encountering a stop codon (p.(Ala450ProfsTer164)). This variant, located in exon 10 of 10, is predicted to cause loss of a stop codon and result in an elongated protein. The additional residues are expected to cause improper folding, resulting in loss of function in a gene in which loss-of-function is an established disease mechanism (PVS1; PMID 19790256). This variant is absent in gnomAD v2.1.1 (PM2_Supporting). This variant was identified in an individual with a clinical history highly consistent with GCK-MODY; however, there was insufficient clinical information to evaluate for PP4. In summary, the c.1348del variant meets the criteria to be classified as pathogenic for monogenic diabetes. ACMG/AMP criteria applied, as specified by the ClinGen MDEP (specification version 1.3.0, approved 8/11/2023): PVS1, PP4, PM2_Supporting.