The NM_000020.3: c.1445C>T variant in ACVRL1 is a missense variant predicted to cause substitution of alanine by valine at amino acid 482 (p.Ala482Val). Another missense variant, c.1445C>A, Ala482Glu (PMID: 17786384, 21158752), in the same codon has been classified as likely pathogenic for autosomal dominant Hereditary Hemorrhagic Telangiectasia by the ClinGen Hereditary Hemorrhagic Telangiectasia Variant Curation Expert Panel (PM5). However, the filtering allele frequency (the lower threshold of the 95% CI of 395/129122) of the c.1445C>T variant in ACVRL1 is 0.002819 for European (non-Finnish) chromosomes by gnomAD v2.1.1, which is higher than the ClinGen Hereditary Hemorrhagic Telangiectasia Variant Curation Expert Panel threshold (>0.002) for BS1, and therefore meets this criterion (BS1). This variant has also been observed in 3 patients with an alternate molecular basis for disease (patients also carry a likely pathogenic/pathogenic ENG variant) (BP5; PMID: 15517393, Internal lab contributors). The computational predictor REVEL gives a score of 0.839, which is above the threshold of ≥0.644, evidence that correlates with impact to ACVRL1 function (PP3). However, functional assays (BRE assay, Western blot analysis of Smad1/5 phosphorylation) in NIH-3T3 cells showed that the variant protein responded to BMP9 stimulation either measured in the BRE assay or by Smad1/5 phosphorylation, indicating that this variant does not impact protein function (BS3_Supporting; PMID: 20501893). In summary, this variant meets the criteria to be classified as likely benign for autosomal dominant hereditary hemorrhagic telangiectasia based on the ACMG/AMP criteria applied, as specified by the ClinGen Hereditary Hemorrhagic Telangiectasia Variant Curation Expert Panel: BS1, BP5, BS3_Supporting, PP3, PM5 (specification version 1.0.0; 1/4/2024).