Cystic fibrosis (CF) is a life-limiting disorder of fluid and electrolyte transport affecting 70,000 individuals worldwide. Patients with CF carry loss of function mutations in each CF Transmembrane conductance Regulator (CFTR) gene. CFTR encodes a cAMP-activated chloride channel that is critical for proper hydration of mucous secretions in the pulmonary airways and pancreatic ducts and maintaining the correct concentration of chloride in sweat. Recently, treatment of CF has taken a major step forward with successful clinical trials of Kalydeco (VX-770), a potentiator compound that increases the function of CFTR bearing the G551D mutation (~2-3% of CF alleles) leading to reduced sweat chloride concentration ([Cl-]) and improved lung function measurements. The success of Kalydeco has fostered the development of numerous other compounds that can correct misfolded forms of mutant CFTR ("correctors") and additional compounds that "potentiate" CFTR that does not conduct chloride at wildtype levels. We now stand at the threshold of being able to treat CF at its root cause;however, there are substantial challenges in delivering molecular therapy to all CF patients. First, there are many different missense and in frame deletion mutations in CFTR (n=816) that a clinical trial for each mutation is not feasible. Second, we don't know if transient increase in CFTR function translates into long-term improvement in lung disease, the major cause of mortality in CF. Third, as lung disease in CF proceeds over many years, we need to gauge effectiveness of CFTR-directed treatment using 'short-term'clinical endpoints. Key preliminary observations suggest that we can address each challenge. CF-causing missense and in frame deletion mutations (n = 47) clustered into groups according to their effect on folding and/or chloride conduction of CFTR appear to correspond to corrector or potentiator responsiveness. Analysis of ~23,000 patients in the CFTR2 database (cftr2.org) revealed that CFTR chloride channel function (as % of wildtype) transformed to a logarithmic scale correlates with cross-sectional lung function (r = 0.43;p = 0.002) and with sweat [Cl-] (r = 0.80;p= 1.3 x 10-11). The overall goal of this application is to inform treatment of CF with CFTR-directed therapies by advancing our understanding of the relationship between CFTR function and clinical manifestations. This goal will be achieved by 1) Classifying CF-causing mutations according to their effect on folding and/or conduction to assess their likely response to current and future CFTR-directed therapeutics;2) Determining the extent to which longitudinal lung function correlates with in vitro CFTR molecular defects and 3) Determining if longitudinal measures of lung function correlate with in vivo CFTR function as measured by sweat [Cl-]. Upon completion of these aims, we will have mined the CFTR2 database and correlated phenotype data with in vitro properties of CFTR mutants to maximize the number of CF patients eligible for CFTR-directed therapy, to estimate the benefit of molecular therapy on long-term lung function in CF patients and to validate the use of sweat gland function to monitor the effectiveness of CFTR-directed treatment.

Public Health Relevance

Cystic Fibrosis (CF) is a life-limiting disorder caused by mutations in the CFTR gene that affects 70,000 individuals worldwide. The overall goal of this proposal is to understand the consequences of different mutations upon the function of CFTR and the severity of CF. This information will be invaluable in predicting outcome for CF patients and evaluating the potential of therapies targeted at specific mutations in CFTR.

Agency
National Institute of Health (NIH)
Institute
National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Type
Research Project (R01)
Project #
2R01DK044003-23A1
Application #
8631164
Study Section
Genetics of Health and Disease Study Section (GHD)
Program Officer
Mckeon, Catherine T
Project Start
1991-05-01
Project End
2018-04-30
Budget Start
2013-09-15
Budget End
2014-04-30
Support Year
23
Fiscal Year
2013
Total Cost
$405,000
Indirect Cost
$155,000
Name
Johns Hopkins University
Department
Genetics
Type
Schools of Medicine
DUNS #
001910777
City
Baltimore
State
MD
Country
United States
Zip Code
21218
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Collaco, Joseph M; Blackman, Scott M; Raraigh, Karen S et al. (2016) Sources of Variation in Sweat Chloride Measurements in Cystic Fibrosis. Am J Respir Crit Care Med 194:1375-1382
Gottschalk, Laura B; Vecchio-Pagan, Briana; Sharma, Neeraj et al. (2016) Creation and characterization of an airway epithelial cell line for stable expression of CFTR variants. J Cyst Fibros 15:285-94
Lee, Melissa; Vecchio-Pagán, Briana; Sharma, Neeraj et al. (2016) Loss of carbonic anhydrase XII function in individuals with elevated sweat chloride concentration and pulmonary airway disease. Hum Mol Genet 25:1923-1933
Sosnay, Patrick R; Castellani, Carlo; Penland, Christopher M et al. (2016) Bias in CFTR screening panels. Genet Med 18:209
Cutting, Garry R (2015) Cystic fibrosis genetics: from molecular understanding to clinical application. Nat Rev Genet 16:45-56
Masica, David L; Sosnay, Patrick R; Raraigh, Karen S et al. (2015) Missense variants in CFTR nucleotide-binding domains predict quantitative phenotypes associated with cystic fibrosis disease severity. Hum Mol Genet 24:1908-17
Sharma, Neeraj; Sosnay, Patrick R; Ramalho, Anabela S et al. (2014) Experimental assessment of splicing variants using expression minigenes and comparison with in silico predictions. Hum Mutat 35:1249-59
Cutting, Garry R (2014) Annotating DNA variants is the next major goal for human genetics. Am J Hum Genet 94:5-10
Pittman, Jessica E; Cutting, Garry; Davis, Stephanie D et al. (2014) Cystic fibrosis: NHLBI Workshop on the Primary Prevention of Chronic Lung Diseases. Ann Am Thorac Soc 11 Suppl 3:S161-8

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