The c.1548C>T variant in the HNF1 homeobox A gene, HNF1A, is a synonymous (silent) variant at codon 516 (p.(Gly516=)) of NM_000545.8. This variant has a minor allele frequency of 0.0000088 in the gnomAD v2.1.1 European non-Finnish population and no copies in another subpopulation, which is less than the ClinGen MDEP threshold for PM2_Supporting (≤0.00002 and ≤1 copy in any other subpopulation) (PM2_Supporting). BP7 was not applied for this synonymous variant because SpliceAI predicts an impact on splicing, specifically a gain of a novel splice acceptor site (score = 0.47); however, PP3 was not applied because an acceptor loss was not predicted (score = 0.03). In summary, c.1548C>T 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.