 A very small proportion (those affected by SMAD4 ( MADH4) mutations, see below ) have multiple benign polyps in the large intestine, which may bleed or transform into colorectal cancer. A similarly small proportion experiences pulmonary hypertension, a state in which the pressure in the lung arteries is increased, exerting pressure on the right side of the heart and causing peripheral edema (swelling of the legs), fainting and attacks of chest pain. It has been observed that the risk of thrombosis (particularly venous thrombosis, in the form of deep vein thrombosis or pulmonary embolism) may be increased. There is a suspicion that those with HHT may have a mild immunodeficiency and are therefore at a slightly increased risk from infections.
