Table 3– Updated clinical classification of pulmonary hypertension (PH)
1. PAH
 1.1. Idiopathic PAH
  1.2.1 BMPR2 gene mutation
  1.2.2 ALK1, endoglin (with or without hereditary haemorrhagic telangiectasia) gene mutation
  1.2.3 Unknown
 1.3. Drug- and toxin-induced
 1.4. APAH
  1.4.1. Connective tissue diseases
  1.4.2. HIV infection
  1.4.3. Portal hypertension
  1.4.4. Congenital heart disease
  1.4.5. Schistosomiasis
  1.4.6. Chronic haemolytic anaemia
 1.5. Persistent PH of the newborn
1′. Pulmonary veno-occlusive disease and/or pulmonary capillary haemangiomatosis
2. PH due to left heart disease
 2.1. Systolic dysfunction
 2.2. Diastolic dysfunction
 2.3. Valvular disease
3. PH due to lung diseases and/or hypoxia
 3.1. Chronic obstructive pulmonary disease
 3.2. Interstitial lung disease
 3.3. Other pulmonary diseases with mixed restrictive and obstructive pattern
 3.4. Sleep-disordered breathing
 3.5. Alveolar hypoventilation disorders
 3.6. Chronic exposure to high altitude
 3.7. Developmental abnormalities
5. PH with unclear and/or multifactorial mechanisms
 5.1. Haematological disorders: myeloproliferative disorders and splenectomy
 5.2. Systemic disorders, sarcoidosis, pulmonary Langerhans cell histiocytosis, lymphangioleiomyomatosis, neurofibromatosis and vasculitis
 5.3. Metabolic disorders: glycogen storage disease, Gaucher disease and thyroid disorders
 5.4. Others: tumoural obstruction, fibrosing mediastinitis and chronic renal failure on dialysis
  • PAH: pulmonary arterial hypertension; BMPR2: bone morphogenetic protein receptor, type 2; ALK1: activin receptor-like kinase 1; APAH: associated PAH; CTEPH: chronic thromboembolic PH.