For a general phenotypic description and a discussion of genetic heterogeneity of pulmonary surfactant metabolism dysfunction, see SMDP1 (265120).

Dyskeratosis congenita and related telomere biology disorders (DC/TBD) are caused by impaired telomere maintenance resulting in short or very short telomeres. The phenotypic spectrum of telomere biology disorders is broad and includes individuals with classic dyskeratosis congenita (DC) as well as those with very short telomeres and an isolated physical finding. Classic DC is characterized by a triad of dysplastic nails, lacy reticular pigmentation of the upper chest and/or neck, and oral leukoplakia, although this may not be present in all individuals. People with DC/TBD are at increased risk for progressive bone marrow failure (BMF), myelodysplastic syndrome or acute myelogenous leukemia, solid tumors (usually squamous cell carcinoma of the head/neck or anogenital cancer), and pulmonary fibrosis. Other findings can include eye abnormalities (epiphora, blepharitis, sparse eyelashes, ectropion, entropion, trichiasis), taurodontism, liver disease, gastrointestinal telangiectasias, and avascular necrosis of the hips or shoulders. Although most persons with DC/TBD have normal psychomotor development and normal neurologic function, significant developmental delay is present in both forms; additional findings include cerebellar hypoplasia (Hoyeraal Hreidarsson syndrome) and bilateral exudative retinopathy and intracranial calcifications (Revesz syndrome and Coats plus syndrome). Onset and progression of manifestations of DC/TBD vary: at the mild end of the spectrum are those who have only minimal physical findings with normal bone marrow function, and at the severe end are those who have the diagnostic triad and early-onset BMF.

Dyskeratosis congenita and related telomere biology disorders (DC/TBD) are caused by impaired telomere maintenance resulting in short or very short telomeres. The phenotypic spectrum of telomere biology disorders is broad and includes individuals with classic dyskeratosis congenita (DC) as well as those with very short telomeres and an isolated physical finding. Classic DC is characterized by a triad of dysplastic nails, lacy reticular pigmentation of the upper chest and/or neck, and oral leukoplakia, although this may not be present in all individuals. People with DC/TBD are at increased risk for progressive bone marrow failure (BMF), myelodysplastic syndrome or acute myelogenous leukemia, solid tumors (usually squamous cell carcinoma of the head/neck or anogenital cancer), and pulmonary fibrosis. Other findings can include eye abnormalities (epiphora, blepharitis, sparse eyelashes, ectropion, entropion, trichiasis), taurodontism, liver disease, gastrointestinal telangiectasias, and avascular necrosis of the hips or shoulders. Although most persons with DC/TBD have normal psychomotor development and normal neurologic function, significant developmental delay is present in both forms; additional findings include cerebellar hypoplasia (Hoyeraal Hreidarsson syndrome) and bilateral exudative retinopathy and intracranial calcifications (Revesz syndrome and Coats plus syndrome). Onset and progression of manifestations of DC/TBD vary: at the mild end of the spectrum are those who have only minimal physical findings with normal bone marrow function, and at the severe end are those who have the diagnostic triad and early-onset BMF.

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) (review by Gross and Hunninghake, 2001; summary by Legendre et al., 2020). Idiopathic pulmonary fibrosis is one of a family of idiopathic pneumonias sharing clinical features of shortness of breath, radiographically evident diffuse pulmonary infiltrates, and varying degrees in inflammation, fibrosis, or both on lung biopsy. In some cases, the disorder can be rapidly progressive and characterized by sequential acute lung injury with subsequent scarring and end-stage lung disease. Although older studies included several forms of interstitial pneumonia under the term 'idiopathic pulmonary fibrosis,' the clinical label of 'idiopathic pulmonary fibrosis' should be reserved for patients with a specific form of fibrosing interstitial pneumonia referred to as usual interstitial pneumonia (Gross and Hunninghake, 2001). It is estimated that 0.5 to 2.2% of cases of idiopathic pulmonary fibrosis are familial (Marshall et al., 2000). Gross and Hunninghake (2001) reviewed idiopathic pulmonary fibrosis, emphasizing definition, pathogenesis, diagnosis, natural history, and therapy. Antoniou et al. (2004) provided a 'top ten list' of references pertaining to etiopathogenesis, prognosis, diagnosis, therapy, and other aspects of idiopathic pulmonary fibrosis. For a discussion of genetic heterogeneity of ILD, see ILD1 (619611). Pulmonary fibrosis can also be a feature in patients with mutations in the TERT (187270) or the TERC (602322) gene; see PFBMFT1 (614742) and PFBMFT2 (614743). Some patients with surfactant protein C deficiency (610913) who survive to adulthood manifest features of pulmonary fibrosis.

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.

Telomere-related pulmonary fibrosis and/or bone marrow failure syndrome-8 (PFBMFT8) is an autosomal dominant disorder characterized by the onset of progressive pulmonary fibrosis in adulthood. Some affected individuals have signs of bone marrow failure, such as thrombocytopenia, or liver dysfunction, including hepatopulmonary syndrome. Other features of dyskeratosis congenita, including premature graying of the hair, may be observed. Telomeres are shortened compared to controls (Kelich et al., 2022). For a discussion of genetic heterogeneity of telomere-related pulmonary fibrosis and/or bone marrow failure, see PFBMFT1 (614742).