ACVRL1 and juvenile polyposis syndrome: For example, patients living with the autosomal dominant hereditary hemorrhagic telangiectasia (HHT) (HHT1; OMIM: #187300/HHT2; OMIM: #600376/Juvenile polyposis/HTT syndrome; OMIM: #175050) can remain undiagnosed, despite extensive genetic testing considering the coding regions of known HHT genes.