Journal
AMERICAN JOURNAL OF RESPIRATORY CELL AND MOLECULAR BIOLOGY
Volume 57, Issue 6, Pages 711-720Publisher
AMER THORACIC SOC
DOI: 10.1165/rcmb.2017-0166OC
Keywords
cystic fibrosis; ENaC; epithelial sodium channel; genetic modifier; SCNN1D
Funding
- National Institute of Arthritis and Musculoskeletal and Skeletal Diseases, National Institutes of Health (NIH) [R01 AR068429]
- Shriver National Institute of Child Health and Human Development, National Human Genome Research Institute, NIH [U19 HD077671]
- Gene Discovery Core of The Manton Center for Orphan Disease Research, Boston Children's Hospital
- Slika Family Fund
- May Family Fund
- NIH [U54 HD090255, RO1 HL090136, U01 HL100402 RFA-HL-09-004, P30 DK079307]
- Cystic Fibrosis Foundation Therapeutics, Inc. [KIM15XX0, LIH15XX0]
- National Heart, Lung, and Blood Institute, NIH [R37HL51856]
- CFMS Fund
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Cystic fibrosis (CF) remains the most lethal genetic disease in the Caucasian population. However, there is great variability in clinical phenotypes and survival times, even among patients harboring the same genotype. We identified five patients with CF and a homozygous F508del mutation in the CFTR gene who were in their fifth or sixth decade of life and had shown minimal changes in lung function over a longitudinal period of more than 20 years. Because of the rarity of this long-term nonprogressive phenotype, we hypothesized these individuals may carry rare genetic variants in modifier genes that ameliorate disease severity. Individuals at the extremes of survival time and lung-function trajectory underwent whole-exome sequencing, and the sequencing data were filtered to include rare missense, stopgain, indel, and splicing variants present with a mean allele frequency of,0.2% in general population databases. Epithelial sodium channel (ENaC) mutants were generated via site-directed mutagenesis and expressed for Xenopus oocyte assays. Four of the five individuals carried extremely rare or never reported variants in the SCNN1D and SCNN1B genes of the ENaC. Separately, an independently enriched rare variant in SCNN1D was identified in the Exome Variant Server database associated with a milder pulmonary disease phenotype. Functional analysis using Xenopus oocytes revealed that two of the three variants in d- ENaC encoded by SCNN1D exhibited hypomorphic channel activity. Our data suggest a potential role for d- ENaC in controlling sodium reabsorption in the airways, and advance the plausibility of ENaC as a therapeutic target in CF.
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