The c.1332del variant in the glucokinase gene, GCK, causes a frameshift in the protein at codon 445 (NM_000162.5), adding 169 novel amino acids before encountering a stop codon (p.(Ser445ValfsTer169)). 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). Additionally, this variant is absent from gnomAD v2.1.1 (PM2_Supporting). This variant was identified in two unrelated individuals with a clinical picture consistent with monogenic diabetes, however PS4_Moderate cannot be applied because this number is below the MDEP threshold, and PP4 could not be evaluated due to lack of clinical information (ClinVar ID 36197, internal lab contributor). In summary, the c.1332del variant meets the criteria to be classified as likely pathogenic for monogenic diabetes. ACMG/AMP criteria applied, as specified by the ClinGen MDEP (specification version 1.2.0, approved 6/7/2023): PVS1, PM2_Supporting.