The c.694C>G variant in the HNF1 homeobox A gene, HNF1A, causes an amino acid change of leucine to valine at codon 232 (p.(Leu232Val)) of NM_000545.8. This variant is located within a conserved region of the DNA binding domain (codons 107-174 and 201-280) of HNF1A, which is defined as critical for the protein’s function by the ClinGen MDEP (PM1_Supporting) and is absent from gnomAD v2.1.1 (PM2_Supporting). This variant has a REVEL score of 0.688, which is between the ClinGen MDEP thresholds for BP4 and PP3, predicting neither a damaging nor benign impact on HNF1A function. 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 HNF1A-monogenic diabetes (MODY probability calculator result >50%, negative genetic testing for HNF4A) (PP4; internal lab contributors). This variant segregated with diabetes, with 3 informative meioses in 1 family (PP1; internal lab contributors). Another missense variant, c.695T>C p.Leu232Pro, has been classified as likely pathogenic by the ClinGen MDEP (PM5_Supporting). In summary, c.694C>G meets the criteria to be classified as likely pathogenic for monogenic diabetes. ACMG/AMP criteria applied, as specified by the ClinGen MDEP (specification version 2.1.0, approved 8/11/2023): PP4_Moderate, PP1, PM1_Supporting, PM2_Supporting, PM5_Supporting.