The c.871C>G variant in the HNF1 homeobox A gene, HNF1A, causes an amino acid change of proline to alanine at codon 291 (p.(Pro291Ala)) of NM_000545.8. This variant was identified in 4 unrelated individuals with non- autoimmune and non-absolute/near-absolute insulin-deficient diabetes (PS4_Moderate; internal lab contributors). Also, this variant has a minor allele frequency of 0.000009234 in the gnomAD v2.1.1 European non-Finnish population which is less than the ClinGen MDEP threshold for PM2_Supporting (≤0.00002 and ≤1 copy in any other subpopulation) (PM2_Supporting). This variant was identified in an individual with a clinical history highly specific for HNF1A-MODY (MODY probability calculator result >50%, negative genetic testing for HNF4A) (PP4; internal lab contributors). Additionally, this variant was identified in a patient with different HNF1A variant curated by MDEP as pathogenic (BP2; internal lab contributors). This variant was identified in a normoglycemic individual >70 years old, and the expected penetrance for HNF1A-MODY is 95% by age 70 (BS2; internal lab contributors). This variant has a REVEL score of 0.28, which is between the ClinGen MDEP thresholds, predicting neither a damaging nor benign impact on HNF1A function. In summary, c.871C>G meets the criteria to be classified as a variant of uncertain significance for monogenic diabetes. ACMG/AMP criteria applied, as specified by the ClinGen MDEP (specification version 1.1, approved 9/30/2021): PS4_Moderate, PM2_Supporting, PP4, BP5, BS2