1. CFTR2 – Part 2 Using CFTR2 to examine how CFTR mutations affect clinical outcome
Patrick Sosnay on behalf of the CFTR2 team
Johns Hopkins University
Perdana University Graduate School of Medicine

2. CFTR Mutations
Cystic Fibrosis
Genotype
Phenotype

3. CFTR Mutations Cystic Fibrosis CFTR Gene CFTR Protein Epithelial Cells
Organs
Clinical Traits

4. Pancreatic status differs by the type of mutation
Mutation Type
Example
“severe”
Pancreatic Insufficient
“mild”
Pancreatic Sufficient
Missense
G551D, R347H 
Single amino acid deletion
F508del
Stop Codon
G542X
Splice Junction
1717-1G>A
Frameshift
3659delC
Kristidis P, Bozon D, Corey M et al. Am J Hum Genet

5. Pancreatic status can be predicted from mutation class
CFTR
I. RNA Expression
II. Folding and modification
IV. Channel function
V. Reduced expression
III. Channel activation
Welsh and Smith, Cell, 1993 PS
Golgi
Rough
endoplasmic
reticulum
Nucleus PI

6. Incomplete correlation between genotype and phenotype
Good correlation with pancreatic status (insufficient vs. sufficient)
Moderate correlation with sweat chloride concentration when patients are grouped according to pancreatic status
Weak correlation with lung function

7. Individual mutations do not appear to correlate with lung function
The Cystic Fibrosis Genotype-Phenotype Consortium NEJM 1993

8. Specific Genotype
Specific Trait
Mutations grouped by type or class
Discrete variable: Pancreatic sufficient or pancreatic insufficient

9. ? Specific Genotype Specific Trait
Continuous variable: Sweat chloride or lung function
Individual mutations

10. Clinical Data from CFTR2

11. Continuous variable: Sweat chloride or lung function
CFTR Gene
CFTR Protein
Epithelial Cells
Organs
Clinical Traits
Use CFTR function measurements in cell lines as a way of describing genotype
Specific Genotype
Specific Trait
Continuous variable: Sweat chloride or lung function
1100 mutations in CFTR2

12. CFTR chloride channel function correlates with sweat chloride concentration of patients that carry the same mutations
R1070Q
M470V
I148T

13. CFTR chloride channel function correlates with sweat chloride concentration of patients that carry the same mutations

14. The relationship between log10 CFTR function and sweat chloride is linear
r=0.78, p<0.001

15. The relationship between log10 CFTR function and lung function is linear
r=0.56, p<0.001

16. Consequences of exponential relationship on lung function and sweat chloride concentration
Mean lung function increases 8% predicted (95% CI 4-12)
0- 5% function
Mean sweat Chloride decreases 27 mEq/L (95% CI 20-33)

17. Consequence of exponential relationship on lung function and sweat chloride concentration
Mean lung function increases 1.4% predicted (95% CI )
Mean sweat chloride decreases 4.7 mEq/L (95% CI )
5- 10% function

18. Environment Other genes
Why is there greater change in sweat chloride than in lung function with restoration of CFTR function?
CFTR Gene
CFTR Protein
Epithelial Cells
Organs
Clinical Traits
Environment
Other genes
CFTR channel function plays a greater role in determining sweat chloride concentration than FEV1

19. Opportunities for future studies
Collection of clinical data from patients in other regions
To examine global variability
To inform disease liability of rare variants
Correlate genotype with longitudinal measures of lung function and other complications of CF (e.g. lung infection)
Examine the relationship of other CFTR functions (e.g. ENaC regulation, HCO3- transport) with sweat chloride concentration, pancreatic status, and lung function

20. Summary
Data from nearly 40,000 CF patients in the CFTR2 database has been instrumental in:
Increasing the list of clinically, functionally and genetically vetted ‘CF-causing’ mutations from 23 to ~160 (more to follow..)
Demonstrating that CFTR chloride channel function displays an exponential relationship with sweat chloride concentration and lung function.
Revealing that improvement in low function CFTR mutations will have the greatest effect on CF phenotype.

21. With tremendous gratitude
Chris Penland
Preston Campbell
Bruce Marshall
Leslie Hazle
Cindy George
Bob Beall
Mentors:
Garry Cutting
Rachel Karchin
Charlie Wiener
JHH CF Team: Michael Boyle, Noah Lechtzin, Christian Merlo, Meghan Ramsay, Sue Sullivan, Marsha Davis, Rebecca Smith, Karen VonBerg, Kathie Bukowski
CFTR2 Team:
Michelle Lewis
Karen Siklosi
Johanna Rommens
Mary Corey
Ruslan Dorfman
Julian Zielenski
Carlo Castellani
Fred Van Goor
Phil Thomas, Margarida Amaral, Claude Ferec, Milan Macek, Phil Farrell
Adi Gherman, Kyle Kaniecki, Jessica LaRusch, Darci Ferrer, Dave Masica, Kathleen Naughton, Neeraj Sharma