Inherited Respiratory System

Disorders

Cystic Fibrosis (CF)

CF is the most common life-limiting autosomal recessive disorder in white population.

CF is chronic, progressive, and frequently fatal genetic disease of the mucous glands.

Affects the respiratory and digestive systems in children and young adults.

An average person has a lifespan of 40 years with the right treatment.

Cystic Fibrosis

• Cystic Fibrosis is caused by a defective CFTR gene which codes for a Na+ and Cl- transporter found on the surface of epithelial cells of lungs and other organs.

• CFTR - Cystic Fibrosis Transmembrane conduction Regulator

Cystic Fibrosis• Autosomal recessive• Gene cloned in 1989:

“CFTR”• 1601 mutations in

CFTR known to cause CF

• An extensive amount of information is known about CFTR

Science, September 1989

Pathophysiology of CF

CFTR Mutation

Epithelial cell dysfunction

Disease manifestations• Lungs• Sinuses• Pancreas• Liver• Biliary duct• Bones• Vas deferens

?

CF Lung

Chloride does not get into airway; more sodium leaves; mucus is thick

Airway Cross Sectional View

Knowles & Boucher 2002;109:571

Epithelial cell layer

Mucus layer

Pericellular layerwith cilia

Required Geometry for Effective Mucociliary Clearance

Knowles & Boucher 2002;109:571

Consequences of CFTR Deficiency on Airway Clearance

Knowles & Boucher 2002;109:571

Pathophysiology of CF Lung Disease

CF Gene Mutation

Ion Transport Abnormalities

Altered AirwayEnvironment

Inflammation Infection

TissueDamage

R. Simon

Pathophysiology of CFLung Disease

Bronchiectasis

Death

Chronic RespiratoryFailure

CF Gene Mutation

Recurrent Bronchitis

Source Undetermined

R. Simons

Clinical Manifestations

Respiratory Tract

• Cough is the most constant symptom.

• Wheezing

• Recurrent chest infection

• Cyanosis is a late sign

• Atelactasis, hemoptysis, pneumothorax, and cor pulmonale

• Sinusitis, nasal polyps

Clinical Manifestations….

Intestinal Tract

1. Meconium ileus 10-20%

2. Meconium plug syndrome (meconium ileus equivalent)…more than 85% of patients showed evidence of maldigestion from exocrine pancreatic insufficiency.

3. Bile or acid reflux with oesophagitis

4. Sub acute appendicitis

5. Rectal prolapse

6. Failure to thrive

7. Fat-soluble vitamin deficiency manifestation.

Clinical Manifestations…

Biliary Tract

• Biliary cirrhosis symptomatic in 2-3% .

• Ascitis, Jaundice, hematemesis, esophageal varices

• Neonatal hepatitis

Clinical Manifestations…

• Diabetes Mellitus… 8% after the age of 10.

• 95% of males are azoospermic because of failure of development of wolffian duct structure.

• Secondary amenorrhea

• Cervicitis

• Hypochloremic alkalosis

Diagnostic criteria for CF

At least one of the following:

1) One or more clinical manifestations of CF• Meconium ileus• Chronic bronchitis / bronchiectasis• Chronic infection of the paranasal sinuses• Pancreatic insufficiency• Salt loss syndromes• Male infertility due to congenital bilateral

absence of the vas deferens

2) History of CF in a sibling

Diagnostic Criteria for CF

At least one of the following:

1) Elevated sweat chloride test

2) Identification of a mutation in each CFTR gene known to cause CF

The Sweat Test

“Gold Standard” for testing over 40

years

- painless

- inexpensive

- gives definite answers

Results;

• Cl- ≥ 60 mEq/L Positive

• 40-60 mEq/L ?

Genotyping for CF Diagnosis

• 1601 CFTR mutations known to cause CF

• Only 25 mutations have a frequency > 0.1%

Frequency, %

0 10 20 30 40 50 60 70

R347P3849+10kbC T

Δ I507R117H

R1162X1717-1G A

R553X621+1G T

W1282XN1303KG551DG542XΔF508

CF Genetic Analysis Consortium

Population Frequency of Specific CFTR Mutations Causing CF

Genotyping for CF Diagnosis

• Current commercial screening tests

• Look for presence of between 25 - 100 mutations

• These will detect a CF allele only ~90% of time

• For a group of patients with known CF, genotyping would be diagnostic in only ~81% of patients

• Screening for most common mutations is not as sensitive as sweat testing (98%) to diagnose classic CF

Genetic Diagnosis of CF

• Tests becoming commercially available for detecting mutations more broadly• PCR used to amplify all exons and surrounding

splice sites

• Heteroduplex formation screening and/or sequencing

• Analysis for large deletions and duplications

• Cost ~ $2,500

CF: A Disease for aMultidisciplinary Team

The Principles of management:

1. To Allow the child and his family, as far as possible, to enjoy a normal lifestyle.

2. To minimize the emotional problems that invariably develop.

3. To prevent, or at least retard as far as possible, progressive lung disease.

4. To achieve optimal nutrition and maintain normal growth

CF Treatment

• PHYSIOTHERAPY and physical activity

• ANTIBIOTIC THERAPY

• BRONCHODILATOR THERAPY• Beta2 agonist

• ANT-INFLAMMATORY AGENTS• Corticosteroids for Bronchopulmopnary aspergillosis

• TREATMENT OF PULMONARY COMPLICATIONS

Hereditary Pulmonary Emphysema“alpha1 antitrypsin deficiency”

• Emphysema - abnormal permanent enlargement of the airspace distal to the terminal bronchioles, accompanied by destruction of their walls and without obvious fibrosis.

• Hereditary deficiency of α1-antitrypsin inhibitor accounts for about 2% of emphysema cases.

• Alpha1 antitrypsin deficiency (AATD) is a autosomal recessive disorder characterized by a predisposition to emphysema and cirrhosis.

Alpha1 antitrypsin is a serin proteinase inhibitor that protect connective tissue of the lungs from the elastase released by leucocytes.

Liver damage arises not from the deficiency of the protease inhibitor, but from pathological polymerization of the variant alpha1-antitrypsin before its secretion from hepatocytes.

More than 75 alleles of the α1-antitrypsin inhibitor gene have been described.

The three main phenotypes are ;MM (normal),

MZ (heterozygous deficiency) and

ZZ (homozygous deficiency).

AATD is a Protein Folding Disease

• Protein folding is the process by which an unfolded polypeptide chain folds in to a specific native and functional structure

• Defective protein folding is an important mechanism underlying the pathogenesis of many diseases

Abnormal Folding and Polymerization of AAT

• The most common and severe form of AAT deficiency is caused by e Z mutation, a single base substitution (Glu-342-lys) in the AAT gene.

• This slows the rate of protein folding in the cell

• Allowing the accumulation of an intermediate which polymerizes Impeeding its release

• Leading to plasma deficiencyAAT Polymer

Pathogenesis of Lung Damage in AATD

Clinical Case

AAT

Lung Related Clinical Manifestations

• Emphysema• Presenting Symptoms:

• Dyspnea (most common symptom)• Cough, phlegm production and wheezing• Bronchodilator responsiveness

• Differences with patients w usual COPD• Earlier Age

• Bullous changes prominent in lung bases• > 90 % of ZZ phenotype have lung bases involved

• Limited to lung bases in 24 %Found exclusively in

• Asthma and Bronchiectasis: • Relationship not proven

Diagnosis

• Measure AAT level

• Mutation analysis

Asthma

• Asthma is a disorder that causes the airways of the lungs to swell and narrow, leading to wheezing, shortness of breath, chest tightness, and coughing.

• Asthma is caused by inflammation in the airways.

Interest in finding a genetic susceptibility locus is based on the heritability that asthma shows.

• Children with one asthmatic parent 3-6 times more likely to develop asthma than a child with two normal parents1.

• Children with two asthmatic parents 10 times more likely to develop asthma than normal1.

Asthma: a complex phenotype

Clinical/Physiological phenotypes

Phenotypes related to triggers

Phenotypes related to inflammation

Severity-definedExacerbation-proneChronic airflow limitationTreatment resistantAge at onset

AspirinEnvironmental. AllergensOccupational AllergensMensesExercise

EosinophilicNeutrophilicPauci-granulocytic

Wenzel, Lancet, 2006

«  Not a single disease entity but made up of various overlapping phenotypes … in people with different genetic predisposition & susceptible to different environmental triggers »OR«  A symptom (as fever): the clinical manifestation of several distinct diseases  

Strategies used to identify genes involved in asthma-related phenotypes

Genome-wide screen approach

Linkage studies ~ 400 genetic markers

(microsatellites)

Genome-wide association studies ~ 300 000 genetic markers (SNP)

Candidate gene approach

Fine mapping AssociationsGene discovery

Biological studiesHypothesis-driven

No Hypothesis

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 X Y

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 X Y

Regions most often replicated across populations

Region Asthma Atopy IgE EOS BHR FEV1

1p31-36 +++++ ++ +++ +

5q31 ++++ ++ ++ +

6p21 ++++ ++ ++++ +++

11q13 + ++ +++ + +

12q21 +++++ + ++ ++

13q12 ++ ++ + + +

Phenotype linked to several regions: polygenic?One region linked to several phenotypes: one pleiotropy gene or several genes in the same region?

> 20 genome screens conducted to date

Populations: Europeans +++, Australians, North-Americans, Chinese, Japanese

GENOME SCAN OF 295 EGEA FAMILIES for 8 asthma-related phenotypes

Bouzigon et al, Hum Mol Genet 2004EOS

IgE MultiRAST

SPT

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 X Y

IgE 12p13

SPT 17q22

FEV1

SPTQ21q21

FEV16q14

FEV1

SPTQAsthma

BR

Candidate gene approach> 500 association studies of asthma phenotypes

(Ober & Hoffjan 2006)

118 genes associated to asthma or atopy phenotypes

54 genes found in 2 to 5 independent studies

15 genes found in 6 to 10 independent studies

10 genes found in > 10 independent studies

IL4, IL13, CD14, IL4RA, ADRB2, HLA-DRB1, HLA-DQB1, TNF, FCER1B, (ADAM33)

Pulmonary Fibrosis associated with known genetic causes

• Neuofibromatosis

• Hermensky Puldak Syndrome

• Gaucher Disease

• Niemann-Pick Disease

• Tuberous sclerosis