ACVRL1 exon 5 codes for the glycine- serine domain, and exons 6–10 code for the kinase domain, all are critical for signaling activity of ACVRL1. Four CTEPH patients had the same point mutation in ACVRL1 exon 10 (c.1450C>G), a variant which had been observed cosegregated with PH in a hereditary hemorrhagic telangiectasia kindred [8]. Here, ACVRL1 is linked to hereditary hemorrhagic telangiectasia.