The c.724del variant in the hepatic nuclear factor 4-alpha gene, HNF4A, causes a frameshift in the protein at codon 242 in NM_175914.5, adding 39 novel amino acids before encountering a stop codon (p.(Val242Cysfs*39)). This variant, located in biologically-relevant exon 7 of 10, is predicted to lead to nonsense mediated decay in a gene in which loss-of-function is an established disease mechanism (PVS1; PMID: 23348805). This variant is absent from gnomAD v2.1.1 (PM2_Supporting). This variant was identified in an individual with a clinical history highly specific for HNF4A-monogenic diabetes (MODY probability calculator result >50%, negative genetic testing for HNF1A) (PP4; internal lab contributors). In summary, c.724del meets the criteria to be classified as pathogenic for monogenic diabetes. ACMG/AMP criteria applied, as specified by the ClinGen MDEP (specification version 2.0.0, approved 10/11/2023): PVS1, PP4, PM2_Supporting.