Inborn errors of pulmonary surfactant metabolism are genetically heterogeneous disorders resulting in severe respiratory insufficiency or failure in full-term neonates or infants. These disorders are associated with various pathologic entities, including pulmonary alveolar proteinosis (PAP), desquamative interstitial pneumonitis (DIP), or cellular nonspecific interstitial pneumonitis (NSIP) (Clark and Clark, 2005). A clinically similar disorder characterized by respiratory distress (267450) can affect preterm infants, who show developmental deficiency of surfactant. Acquired PAP (610910) is an autoimmune disorder characterized by the presence of autoantibodies to CSF2 (138960). Genetic Heterogeneity of Pulmonary Surfactant Metabolism Dysfunction See also SMDP2 (610913), caused by mutation in the SPTPC gene (178620) on 8p21; SMDP3 (610921), caused by mutation in the ABCA3 gene (601615) on 16p13; SMDP4 (300770), caused by mutation in the CSF2RA gene (306250) on Xp22; and SMDP5 (614370), caused by mutation in the CSF2RB gene (138981) on 22q12.

Pulmonary surfactant metabolism dysfunction-5 (SMDP5) is an autosomal recessive lung disorder manifest clinically and pathologically as pulmonary alveolar proteinosis (PAP). PAP is a rare lung disease characterized by the ineffective clearance of surfactant by alveolar macrophages. This results in the accumulation of surfactant-derived lipoproteinaceous material in the alveoli and terminal bronchioles, causing respiratory failure (summary by Greenhill and Kotton, 2009). For a general phenotypic description and a discussion of genetic heterogeneity of pulmonary surfactant metabolism dysfunction, see SMDP1 (265120).

Pulmonary venoocclusive disease primarily affects the postcapillary venous pulmonary vessels and may involve significant pulmonary capillary dilation and/or proliferation. PVOD is an uncommon cause of pulmonary artery hypertension (PPH; see 178600), a severe condition characterized by elevated pulmonary artery pressure leading to right heart failure and death. PVOD accounts for 5 to 10% of 'idiopathic' PPH and has an estimated incidence of 0.1 to 0.2 cases per million. The pathologic hallmark of PVOD is the extensive and diffuse occlusion of pulmonary veins by fibrous tissue, with intimal thickening present in venules and small veins in lobular septa and, rarely, larger veins. Definitive diagnosis of PVOD requires histologic analysis of a lung sample, although surgical lung biopsy is often too invasive for these frail patients. Patients with PVOD respond poorly to available therapy, therefore it is crucial to distinguish PVOD from other forms of PPH. Radiologic characteristics suggestive of PVOD on high-resolution CT of the chest include nodular ground-glass opacities, septal lines, and lymph node enlargement. In addition, because PVOD mainly affects postcapillary vasculature, it causes chronic elevation of pulmonary capillary pressure and thus promotes occult alveolar hemorrhage, which may be a characteristic feature of PVOD (summary by Montani et al., 2008). Genetic Heterogeneity of Pulmonary Venoocclusive Disease See also PVOD2 (234810), caused by mutation in the EIF2AK4 gene (609280) on chromosome 15q15.

Interstitial lung disease (ILD) comprises a heterogeneous group of rare diseases affecting the distal part of the lung and characterized by a progressive remodeling of the alveolar interstitium. The manifestations form a spectrum ranging from idiopathic interstitial pneumonia (IIP) or pneumonitis to the more severe idiopathic pulmonary fibrosis (IPF). IPF is associated with an increased risk of developing lung cancer, which occurs in a subset of patients with ILD. Clinical features of ILD include dyspnea, clubbing of the fingers, and restrictive lung capacity. Imaging typically shows ground glass opacities and inter- and intraseptal thickening, while histologic studies usually show a pattern consistent with 'usual interstitial pneumonia' (UIP) (summary by Nathan et al., 2016, Doubkova et al., 2019). Genetic Heterogeneity of Interstitial Lung Disease See also ILD2 (178500), caused by mutation in the SFTPA2 gene (178642) on chromosome 10q22.