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
CFTR
Mutations
Cystic
Fibrosis
Genotype
Phenotype
CFTR
Mutations
CFTR
Gene
CFTR
Protein
Cystic
Fibrosis
Epithelial
Cells
Organs
Clinical
Traits
Pancreatic status differs by the type of mutation
Mutation
Type
Example
“severe”
Pancreatic
Insufficient
Missense
G551D,
R347H

Single amino
acid deletion
F508del

Stop Codon
G542X

1717-1G>A

3659delC

Splice
Junction
Frameshift
“mild”
Pancreatic
Sufficient

Kristidis P, Bozon D, Corey M et al. Am J Hum Genet. 1992
Pancreatic status can be predicted
from mutation class
CFTR
V. Reduced expression
PS
IV. Channel function
III. Channel activation
Golgi
Rough
endoplasmic
reticulum
II. Folding and modification
I. RNA Expression
Nucleus
Welsh and Smith, Cell, 1993
PI
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
Individual mutations do not appear to
correlate with lung function
100
Pulmonary function
80
60
NS
40
20
0
F508del/F508del R117H/F508del
The Cystic Fibrosis Genotype-Phenotype
Consortium NEJM 1993
Specific Genotype
Mutations grouped
by type or class
Specific Trait
Discrete variable:
Pancreatic sufficient or
pancreatic insufficient
Specific Trait
Specific Genotype
Individual mutations
?
Continuous variable:
Sweat chloride or lung
function
Clinical Data from CFTR2
CFTR
Gene
CFTR
Protein
Epithelial
Cells
Organs
Clinical
Traits
Use CFTR function
measurements in cell lines as a
of describing genotype Specific Trait
Specific way
Genotype
1100 mutations in
CFTR2
Continuous variable:
Sweat chloride or lung
function
100
120
CFTR chloride channel function correlates with
sweat chloride concentration of patients that
carry the same mutations
R1070Q
80
M470V
0
20
40
60
I148T
0
50
100
150
CFTR Function (Chloride Current as % of WT-CFTR)
0
20
40
60
80
100
120
CFTR chloride channel function correlates with
sweat chloride concentration of patients that
carry the same mutations
0
50
100
150
CFTR Function (Chloride Current as % of WT-CFTR)
40
60
80
100
120
The relationship between log10 CFTR function
and sweat chloride is linear
0
20
r=0.78, p<0.001
0.1
1.0
10
CFTR Function (log scale)
100
40
60
80
100
The relationship between log10 CFTR function
and lung function is linear
0
20
r=0.56, p<0.001
0.1
1.0
10
CFTR Function (log scale)
100
Consequences of exponential relationship on
lung function and sweat chloride concentration
40
Mean sweat Chloride
decreases 27 mEq/L (95%
CI 20-33)
20
0- 5% function
0
0
20
40
60
60
80
80
100
100
120
Mean lung function increases 8%
predicted (95% CI 4-12)
0.1
0.1
1.0
1.0
10
10
CFTR
CFTR
Function
Function
(log scale)
(log scale)
100
100
Consequence of exponential relationship on
lung function and sweat chloride concentration
60
80
80
100
100
120
Mean lung function increases
1.4% predicted (95% CI 0.7-2.1)
40
20
5- 10% function
0
0
20
40
60
Mean sweat chloride
decreases 4.7 mEq/L
(95% CI 3.6-5.8)
0.1
0.1
1.0
1.0
10
10
CFTR
CFTR
Function
Function
(log scale)
(log scale)
100
100
Why is there greater change in sweat chloride than in
lung function with restoration of CFTR function?
Environment
CFTR
Gene
CFTR
Protein
Epithelial
Cells
Organs
Other genes
• CFTR channel function plays a greater role in
determining sweat chloride concentration than
FEV1
Clinical
Traits
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
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.
With tremendous gratitude
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
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