The c.526+2dup variant in the HNF1 homeobox A gene, HNF1A, is predicted to remove a canonical splice donor site in intron 2 of NM_000545.8. This variant is absent from gnomAD v2.1.1 (PM2_Supporting). This variant was also identified in an individual with a clinical history highly specific for HNF1A-MODY (MODY probability calculator result >50%, negative genetic testing for HNF4A, and response to low dose sulfonylureas) (PP4_Moderate; internal lab contributors). The computational splicing predictor SpliceAI gives a score of 0.48 for donor loss, predicting that the variant disrupts the donor site of intron 2 of HNF1A (PP3). This variant was identified in three unrelated individuals with non-autoimmune and non-absolute/near-absolute insulin-deficient diabetes; however, PS4_Moderate cannot be applied because this number is below the ClinGen MDEP threshold (internal lab contributors). In summary, c.526+2dup 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): PM2_Supporting, PP4_Moderate, PP3.