CYSTIC FIBROSIS

CYSTIC FIBROSISCYSTIC FIBROSIS

"Woe is the child who tastes salty from a kiss on the brow, for he is cursed, and soon must die.” -Northern European Folklore

Cystic Fibrosis (CF) is a lethal Cystic Fibrosis (CF) is a lethal inherited disease that affects the inherited disease that affects the lungs, digestive system, sweat lungs, digestive system, sweat glands, and male fertilityglands, and male fertility

Its name derives from the fibrous Its name derives from the fibrous scar tissue which develops in the scar tissue which develops in the pancreaspancreas

Figure 8


Cystic Fibrosis affects the body’s ability Cystic Fibrosis affects the body’s ability to move salt and water in and out of a to move salt and water in and out of a cellcell

This results in the lungs and the This results in the lungs and the pancreas secreting a thick mucuspancreas secreting a thick mucus

This mucus blocks passageways and This mucus blocks passageways and prevents proper functionprevents proper function


Hallmarks of CFHallmarks of CF Very salty-tasting skin Very salty-tasting skin Appetite, but poor Appetite, but poor

growth & weight gaingrowth & weight gain Coughing, wheezing & Coughing, wheezing &

shortness of breath shortness of breath Lung infectionsLung infections, e.g. , e.g.

pneumonia/bronchitis pneumonia/bronchitis

Clinical AspectsClinical Aspects

Cystic fibrosis affects the entire bodyCystic fibrosis affects the entire body• Lungs and sinusesLungs and sinuses

• GI, liver and GI, liver and pancreaspancreas

• Endocrine system Endocrine system

• Reproductive systemReproductive system

EpidemiologyEpidemiology

CF is a CF is a rarerare disease disease Approximately 30,000 in the U.S. people have CFApproximately 30,000 in the U.S. people have CF Over 10 million Americans are unknowing carriers.Over 10 million Americans are unknowing carriers. Around 2,500 children with CF are born each year.Around 2,500 children with CF are born each year.

GroupGroup IncidenceIncidence CarriersCarriers Delta F508Delta F508

CaucasiansCaucasians 1 / 3,3001 / 3,300 1 / 291 / 29 70%70%

HispanicsHispanics 1 / 9,0001 / 9,000 1 / 461 / 46 46%46%

African AmericansAfrican Americans 1 / 15,3001 / 15,300 1 / 601 / 60 48%48%

Asian AmericansAsian Americans 1 / 32,1001 / 32,100 1 / 901 / 90 30%30%

CF is a disease of CF is a disease of CaucasiansCaucasians..

HeritabilityHeritabilityCF is a CF is a hereditaryhereditary disease. disease.

Unaffected parents can have Unaffected parents can have children with CF.children with CF.

Males and females are equally Males and females are equally likely to be diagnosed.likely to be diagnosed.

Signs and SymptomsSigns and Symptoms Thick, viscous mucus secretion in the Thick, viscous mucus secretion in the

lungslungs Changes in color and amount of sputumChanges in color and amount of sputum chronic coughingchronic coughing WheezingWheezing BronchitisBronchitis salty skin or poor growthsalty skin or poor growth Weight loss (abdominal swelling)Weight loss (abdominal swelling)

Molecular and Molecular and Genetic Basis of Genetic Basis of Cystic FibrosisCystic Fibrosis

Mapping the gene for CFMapping the gene for CF Gene linkage studies were able to Gene linkage studies were able to

map the mutation to chromosome 7.map the mutation to chromosome 7.

Classical genetics techniques were Classical genetics techniques were not able to accurately pinpoint the not able to accurately pinpoint the mutated gene.mutated gene.

Gene LocusGene LocusChromosome 7; Locus 7q31.2

The CFTR gene:

is 250, 000 bp long

contains 27 exons

the protein has 1, 480 amino acids with a molecular mass of 168, 138 Da

nucleotide of ~ 6,500

Mapping the gene for CFMapping the gene for CF1989:1989: Lap-Chee Tsui, at the Hospital for Sick Children in Lap-Chee Tsui, at the Hospital for Sick Children in

Toronto, clones the Toronto, clones the CFTRCFTR gene. Victory tastes sweet. gene. Victory tastes sweet.

Chromosome Chromosome walkingwalking and and jumping jumping techniques were used techniques were used to identify and sequence the 180,000 bp gene.to identify and sequence the 180,000 bp gene.

The ΔF508 MutationThe ΔF508 Mutation

The mutation results in the deletion of a single The mutation results in the deletion of a single amino acid (Phe) at position 508.amino acid (Phe) at position 508.

A 3 base pair deletion called A 3 base pair deletion called ΔF508ΔF508 is the most is the most common mutation causing cystic fibrosiscommon mutation causing cystic fibrosis

Benefits of ΔF508Benefits of ΔF508The ΔF508 mutation most likely occurred The ΔF508 mutation most likely occurred over 50,000 years ago in over 50,000 years ago in Northern EuropeNorthern Europe..

Individuals with two copies of Individuals with two copies of ΔF508 get cystic fibrosis and often ΔF508 get cystic fibrosis and often cannot reproduce.cannot reproduce.

Having one copy of ΔF508Having one copy of ΔF508 reduces reduces water loss during water loss during choleracholera, greatly , greatly increasing the chance of survival.increasing the chance of survival.

The Function of CFTRThe Function of CFTRCFTR encodes a 170 kDa, membrane-based CFTR encodes a 170 kDa, membrane-based

protein with an active protein with an active transporttransport function function

The CFTR protein plays a vital The CFTR protein plays a vital role in mucus functionrole in mucus function

The CFTR protein helps to keep The CFTR protein helps to keep mucus from becoming thickmucus from becoming thick

Role of CFTR ProteinRole of CFTR Protein

Role of CFTR ProteinRole of CFTR Protein In CF, the CFTR cannot allow chloride In CF, the CFTR cannot allow chloride

ions to move out of the mucus-producing ions to move out of the mucus-producing cellscells

This means water doesn’t leave and it This means water doesn’t leave and it results in the mucus becoming thickresults in the mucus becoming thick

This in turn blocks the passageways, and This in turn blocks the passageways, and allow bacteria to feed off the mucus, allow bacteria to feed off the mucus, which results in more infectionswhich results in more infections

From Mutation to DiseaseFrom Mutation to DiseaseThe mutant form of CFTR The mutant form of CFTR

prevents chloride transport, prevents chloride transport, causing mucus build-upcausing mucus build-up

Mucus clogs the airways Mucus clogs the airways and disrupts the function of and disrupts the function of the pancreas & intestines.the pancreas & intestines.

CFTR MutationsCFTR MutationsOver Over 1,0001,000 mutations in mutations in CFTR have been found.CFTR have been found.

ΔF508 accounts for just ΔF508 accounts for just 70%70% of CF cases. of CF cases.

The Sweat TestThe Sweat Test

Measures the concentration of Measures the concentration of chloridechloride and and sodiumsodium that is excreted in sweat. that is excreted in sweat.

Two reliable positive results on two separate Two reliable positive results on two separate days is diagnostic for CF. days is diagnostic for CF.

Clinical presentation, family history and Clinical presentation, family history and patient age must be considered to interpret patient age must be considered to interpret the results. the results.

5 Classes of CFTR Mutations5 Classes of CFTR MutationsCF Mutations can be classified by the CF Mutations can be classified by the effecteffect they they

have on the CFTR protein.have on the CFTR protein.

5 Classes of CFTR Mutations5 Classes of CFTR Mutations

IDefective

Production

IIDefective

Processing

IIIDefective

Regulation

IVDefective

Conductance

VReduced

Amounts

Genotype Class and MortalityGenotype Class and Mortality

Mutation class can affect disease Mutation class can affect disease mortalitymortality..

Genotype and PhenotypeGenotype and PhenotypeClinical phenotypesClinical phenotypes can vary widely across mutations can vary widely across mutations

Newborn ScreeningNewborn ScreeningInfants can easily be diagnosed with a blood testInfants can easily be diagnosed with a blood test

Elevated levels of trypsinogen indicate CFElevated levels of trypsinogen indicate CF Screening programs identify 10% of cases at birth Screening programs identify 10% of cases at birth

Most hospitals Most hospitals do not screendo not screen for CF at birth. for CF at birth. Should they?Should they?

Genetic Carrier TestingGenetic Carrier Testing Tests for common CF Tests for common CF

mutations are available.mutations are available.

The type of defective CF gene The type of defective CF gene can affect the type of CF can affect the type of CF symptoms.symptoms.

However, genetic testing However, genetic testing cannotcannot fully determine how severe a fully determine how severe a person's CF will be in advance. person's CF will be in advance.

Carrier ScreeningCarrier Screening

Population-based screening: Population-based screening: Particular genetic carrier tests offered to Particular genetic carrier tests offered to

everyone in the general population everyone in the general population Targeted population-based screening: Targeted population-based screening:

Carrier screening limited to particular Carrier screening limited to particular groups of people determined to be at higher groups of people determined to be at higher risk for specific genetic disordersrisk for specific genetic disorders

e.g. Ethnicity-based carrier screeninge.g. Ethnicity-based carrier screening

Carrier TestingCarrier Testing

To determine an individual’s carrier To determine an individual’s carrier status for a specific genetic disease status for a specific genetic disease

Not usually offered on a population Not usually offered on a population basisbasis

Carrier TestingCarrier Testing Available to clients with a family history of Available to clients with a family history of

an autosomal recessive or X-linked genetic an autosomal recessive or X-linked genetic condition for which carrier testing availablecondition for which carrier testing available e.g. Fragile X syndrome, Duchenne muscular e.g. Fragile X syndrome, Duchenne muscular

dystrophy, Hemophilia A or Bdystrophy, Hemophilia A or B

e.g. PKU, Alpha-1-antitrypsin deficiency, e.g. PKU, Alpha-1-antitrypsin deficiency, GalactosemiaGalactosemia

Ethnicity-Based Ethnicity-Based Genetic Genetic

Carrier ScreeningCarrier Screening Purpose: To detect couples at risk for Purpose: To detect couples at risk for

prenatally diagnosable genetic diseasesprenatally diagnosable genetic diseases Types of tests offered based on clients’ Types of tests offered based on clients’

ethnic backgroundethnic background Offered to all individuals of that ethnic Offered to all individuals of that ethnic

background (targeted population screening)background (targeted population screening)

African-AmericanAfrican-American Sickle CellSickle CellCystic FibrosisCystic FibrosisBeta-ThalassemiaBeta-Thalassemia

1 in 101 in 101 in 651 in 651 in 751 in 75

Ashkenazi JewishAshkenazi Jewish Gaucher diseaseGaucher diseaseCystic FibrosisCystic FibrosisTay-Sachs diseaseTay-Sachs diseaseDysautonomiaDysautonomiaCanavan diseaseCanavan disease

1 in 151 in 151 in 26 - 1 in 291 in 26 - 1 in 291 in 301 in 301 in 321 in 321 in 401 in 40

AsianAsian Alpha-ThalassemiaAlpha-ThalassemiaBeta-ThalassemiaBeta-Thalassemia

1 in 201 in 201 in 501 in 50

European AmericanEuropean American Cystic FibrosisCystic Fibrosis 1 in 25 - 1 in 291 in 25 - 1 in 29

French Canadian, CajunFrench Canadian, Cajun Tay Sachs diseaseTay Sachs disease 1 in 301 in 30

HispanicHispanic Cystic FibrosisCystic FibrosisBeta-ThalassemiaBeta-Thalassemia

1 in 461 in 461 in 30 - 1 in 501 in 30 - 1 in 50

MediterraneanMediterranean Beta-ThalassemiaBeta-ThalassemiaCystic FibrosisCystic FibrosisSickle CellSickle Cell

1 in 251 in 251 in 291 in 291 in 401 in 40

Population Condition Carrier Frequency

CARRIER FREQUENCIES BASED ON ETHNIC ORIGIN

CF CF Carrier ResultsCarrier Results Many tests detect a majority but not all carriersMany tests detect a majority but not all carriers

Detection rates differ by ethnicityDetection rates differ by ethnicity Negative results do not eliminate riskNegative results do not eliminate risk

Different mutations may confer different risksDifferent mutations may confer different risks Example: CFTR R117H mutation and 5T allele Example: CFTR R117H mutation and 5T allele

Genetic consultation is available to carriers and Genetic consultation is available to carriers and strongly advised for carrier/carrier couplesstrongly advised for carrier/carrier couples

Carrier Rates: Cystic FibrosisCarrier Rates: Cystic FibrosisEthnic GroupEthnic Group Carrier FrequencyCarrier Frequency Detection RateDetection Rate Carrier risk after Carrier risk after

negative testnegative test

Northern European Northern European CaucasianCaucasian

1/25 – 1/291/25 – 1/29 85-90%85-90% ~1 in 250~1 in 250

Ashkenazi JewishAshkenazi Jewish 1/26 – 1/291/26 – 1/29 97%97% ~1 in 930~1 in 930

Southern European Southern European CaucasianCaucasian

1/291/29 70-80%70-80% ~1 in 97 to 1 in 140~1 in 97 to 1 in 140

HispanicHispanic 1/461/46 57%57% ~1 in 105~1 in 105

African AmericanAfrican American 1/651/65 72%72% ~1 in 232~1 in 232

Asian Asian ~1/90 (?)~1/90 (?) ~30% (?)~30% (?) Not availableNot available

Drug TherapiesDrug Therapies Medication are often aerosolize and can Medication are often aerosolize and can

be inhaledbe inhaled BronchodilatorsBronchodilators MucolyticsMucolytics DecongestantsDecongestants Antibiotics to fight lung infectionsAntibiotics to fight lung infections Enzyme supplementsEnzyme supplements

How can Gene Therapy How can Gene Therapy be used to treat patients be used to treat patients who suffer from Cystic who suffer from Cystic

Fibrosis (CF)?Fibrosis (CF)?

Gene TherapyGene Therapy SmaRT-discovered by Xiaoming LiSmaRT-discovered by Xiaoming Li

Interferes with the processing of RNAInterferes with the processing of RNA Synthesis of DNA probe to locate the geneSynthesis of DNA probe to locate the gene

make copies of normal and abnormal genemake copies of normal and abnormal gene Problems with gene therapyProblems with gene therapy

Ethical issuesEthical issues ““Fooling with Mother Nature”Fooling with Mother Nature”

Gene therapy is currently the most ambitious Gene therapy is currently the most ambitious approach to curing Cystic Fibrosisapproach to curing Cystic Fibrosis

Nondefective copies of the CFTR gene are Nondefective copies of the CFTR gene are introduced into affected cells, where they are introduced into affected cells, where they are taken up and used to create the CFTR taken up and used to create the CFTR proteinprotein

This will result in the mucus functioning This will result in the mucus functioning properly and a stop to Cystic Fibrosisproperly and a stop to Cystic Fibrosis

Gene TherapyGene Therapy

It has been attempted to deliver the normal It has been attempted to deliver the normal CFTR gene to the bronchial epithelium by CFTR gene to the bronchial epithelium by aerosol spray, using a viral vector (usually an aerosol spray, using a viral vector (usually an adenovirus) adenovirus)

This viral vector would contain the genetic This viral vector would contain the genetic material for the CFTR genematerial for the CFTR gene

The vector would be able to enter a cell inside The vector would be able to enter a cell inside the body and insert the genetic material for the the body and insert the genetic material for the CFTR gene into the cells DNACFTR gene into the cells DNA


This would result in the cell having a This would result in the cell having a normal CFTR gene and an end to CFnormal CFTR gene and an end to CF

Thus far the attempts have not been Thus far the attempts have not been completely successful, as most patients completely successful, as most patients develop an immune response against the develop an immune response against the virus during the course of therapyvirus during the course of therapy


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CYSTIC FIBROSIS