NKX2-1mutations leading to surfactant protein promoter dysregulation cause interstitial lung disease in “Brain-Lung-Thyroid Syndrome”

Abstract

NKX2-1 (NK2 homeobox 1) is a critical regulator of transcription for the surfactant protein (SP)-B and -C genes (SFTPB and SFTPC, respectively). We identified and functionally characterized two new de novo NKX2-1 mutations c.493C>T (p.R165W) and c.786_787del2 (p.L263fs) in infants with closely similar severe interstitial lung disease (ILD), hypotonia, and congenital hypothyroidism. Functional analyses using A549 and HeLa cells revealed that NKX2-1-p.L263fs induced neither SFTPB nor SFTPC promoter activation and had a dominant negative effect on wild-type (WT) NKX2-1. In contrast, NKX2-1-p.R165W activated SFTPC, to a significantly greater extent than did WT NKX2-1, while SFTPB activation was only significantly reduced in HeLa cells. In accordance with our in vitro data, we found decreased amounts of SP-B and SP-C by western blot in bronchoalveolar lavage fluid (patient with p.L263fs) and features of altered surfactant protein metabolism on lung histology (patient with NKX2-1-p.R165W). In conclusion, ILD in patients with NKX2-1 mutations was associated with altered surfactant protein metabolism, and both gain and loss of function of the mutated NKX2-1 genes on surfactant protein promoters were associated with ILD in "Brain-Lung-Thyroid syndrome".

An Official American Thoracic Society Clinical Practice Guideline: Classification, Evaluation, and Management of Childhood Interstitial Lung Disease in Infancy

“…The evidence described here is from more than 10 case reports (111,114,115,(161)(162)(163) and case series (110,113,164). The major limitations of the evidence are the study design and that the prevalence of the mutation in patients with this triad of findings has never been estimated; therefore, the yield of testing is uncertain.…”

“…This recommendation is based on case reports and a small case series (115,164) that described children and young adults with mutations in NKX2.1, hypothyroidism, neurologic abnormalities, and pulmonary findings. The recommendation reflects our belief that the benefits of identifying mutations in NKX2.1 (i.e., avoiding the risks and burdens of surgical lung biopsy, patient and family preferences, information to counsel about the potential for familial disease, and anticipatory monitoring for neurological symptoms) justify the cost of genetic testing (Table E1).…”

Heterogeneous Pulmonary Phenotypes Associated With Mutations in the Thyroid Transcription Factor Gene NKX2-1

“…4 Haploinsuffi ciency for NKX2-1 due to either complete gene deletions or loss-of-function mutations results in brain-thyroid-lung syndrome (MIM 610978), with affected individuals having variable degrees of pulmonary disease, thyroid dysfunction, and neurologic abnormalities. [5][6][7][8][9][10][11][12][13][14][15][16][17][18] Neonatal RDS and chronic lung disease in older individuals have been reported in association with NKX2-1 mutations, but the pulmonary phenotype remains incompletely characterized, particularly in older children. Given the role of NKX2-1 in the surfactant system, we hypothesized that individuals with mutations in NKX2-1 may present not only with neonatal RDS, but also with ChILD and evidence of surfactant dysfunction.…”

Extreme phenotypic variability of thyroid dysgenesis in six new cases of congenital hypothyroidism due to PAX8 gene loss-of-function mutations

“…Electrophoretic mobility shift assay (EMSA) was performed as described previously using a biotinylated labeled TPO (5 0 -CTGTCTAAGCTTGAGTGGGCATCA-3 0 ) probe derived from the corresponding promoter, as recommended by the manufacturer (21). For competition incubations, a 100-fold excess of cold probe was used.…”