CFTR2 – Part 2Using CFTR2 to examine how CFTR mutations affect clinical outcome

Patrick Sosnay on behalf of the CFTR2 teamJohns Hopkins University

Perdana University Graduate School of Medicine

CFTR Mutations

Cystic Fibrosis

Genotype Phenotype

CFTR Mutations

Cystic Fibrosis

Pancreatic status differs by the type of mutation

Kristidis P, Bozon D, Corey M et al. Am J Hum Genet. 1992

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

Pancreatic status can be predicted from mutation class

Golgi

Rough endoplasmicreticulum

Nucleus

CFTR

I. RNA Expression

II. Folding and modification

IV. Channel function

V. Reduced expression

III. Channel activation

Welsh and Smith, Cell, 1993

PI

PS

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

0

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F508del/F508del R117H/F508del

Pulmonary function

NS

The Cystic Fibrosis Genotype-Phenotype Consortium NEJM 1993

Discrete variable: Pancreatic sufficient or pancreatic insufficient

Mutations grouped by type or class

Specific GenotypeSpecific Genotype Specific Trait

Specific GenotypeSpecific Genotype Specific Trait

Continuous variable: Sweat chloride or lung function

Individual mutations ?

Clinical Data from CFTR2

1100 mutations in CFTR2

Continuous variable: Sweat chloride or lung function

Specific Trait

Use CFTR function measurements in cell lines as a way of describing genotypeSpecific GenotypeSpecific Genotype

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CFTR chloride channel function correlates with sweat chloride concentration of patients that

carry the same mutations

M470V

I148T

R1070Q

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CFTR chloride channel function correlates with sweat chloride concentration of patients that

carry the same mutations

The relationship between log10 CFTR function and sweat chloride is linear

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r=0.78, p<0.001

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The relationship between log10 CFTR function and lung function is linear

r=0.56, p<0.001

Consequences of exponential relationship on lung function and sweat chloride concentration

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Mean sweat Chloride decreases 27 mEq/L (95% CI 20-33)

Mean lung function increases 8% predicted (95% CI 4-12)

0- 5% function

Consequence of exponential relationship on lung function and sweat chloride concentration

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Mean lung function increases 1.4% predicted (95% CI 0.7-2.1)

5- 10% function

Mean sweat chloride decreases 4.7 mEq/L (95% CI 3.6-5.8)

Why is there greater change in sweat chloride than in lung function with restoration of CFTR function?

• CFTR channel function plays a greater role in determining sweat chloride concentration than FEV1

Environment

Other genes

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

SummaryData 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 gratitudeCFTR2 Team:Michelle LewisKaren SiklosiJohanna RommensMary CoreyRuslan DorfmanJulian ZielenskiCarlo CastellaniFred Van GoorPhil Thomas, Margarida Amaral, Claude Ferec, Milan Macek, Phil FarrellAdi Gherman, Kyle Kaniecki, Jessica LaRusch, Darci Ferrer, Dave Masica, Kathleen Naughton, Neeraj Sharma

Chris PenlandPreston CampbellBruce MarshallLeslie HazleCindy GeorgeBob Beall

Mentors:Garry CuttingRachel KarchinCharlie Wiener

JHH CF Team: Michael Boyle, Noah Lechtzin, Christian Merlo, Meghan Ramsay, Sue Sullivan, Marsha Davis, Rebecca Smith, Karen VonBerg, Kathie Bukowski