Pulmonary arterial hypertension is a progressive disorder characterized by abnormally high blood pressure (hypertension) in the pulmonary artery, the blood vessel that carries blood from the heart to the lungs. Pulmonary arterial hypertension is one form of a broader condition known as pulmonary hypertension. Pulmonary hypertension occurs when most of the very small arteries throughout the lungs narrow in diameter, which increases the resistance to blood flow through the lungs. To overcome the increased resistance, blood pressure increases in the pulmonary artery and in the right ventricle of the heart, which is the chamber that pumps blood into the pulmonary artery. Ultimately, the increased blood pressure can damage the right ventricle of the heart.\n\nSigns and symptoms of pulmonary arterial hypertension occur when increased blood pressure cannot fully overcome the elevated resistance. As a result, the flow of oxygenated blood from the lungs to the rest of the body is insufficient. Shortness of breath (dyspnea) during exertion and fainting spells are the most common symptoms of pulmonary arterial hypertension. People with this disorder may experience additional symptoms, particularly as the condition worsens. Other symptoms include dizziness, swelling (edema) of the ankles or legs, chest pain, and a rapid heart rate.

Primary pulmonary hypertension is a rare progressive disease characterized by increased pulmonary artery pressure in the absence of common causes of pulmonary hypertension, such as chronic heart, lung, or thromboembolic disease. There is often vascular remodeling. The clinical presentation can be nonspecific, and patients often receive a diagnosis late in their clinical course (summary by Ma et al., 2013). For a general phenotypic description and a discussion of genetic heterogeneity of primary pulmonary hypertension, see PPH1 (178600).

Megacystis-microcolon-intestinal hypoperistalsis syndrome-2 (MMIHS2) is characterized by prenatal bladder enlargement, neonatal functional gastrointestinal obstruction, and chronic dependence on total parenteral nutrition and urinary catheterization. The majority of cases have a fatal outcome due to malnutrition and sepsis, followed by multiorgan failure (summary by Wang et al., 2019). For a discussion of genetic heterogeneity of MMIHS, see 249210.