Cystic Fibrosis in Children

1. Overview

Definition and Importance

Cystic fibrosis (CF) is the most common life-limiting autosomal recessive disorder affecting Caucasian populations, with a birth incidence of approximately 1 in 2,500-3,500 live births in populations of Northern European ancestry. [1] The condition results from mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene located on chromosome 7q31.2, leading to defective chloride and bicarbonate transport across epithelial surfaces. [2]

CF is a multisystem disorder affecting exocrine glands throughout the body, but mortality is predominantly driven by progressive bronchiectasis and respiratory failure. The median predicted survival has improved dramatically over the past five decades, from 5 years in the 1960s to over 50 years for children born today, particularly those eligible for CFTR modulator therapy. [3]

The therapeutic landscape has been revolutionised by the development of CFTR modulators, particularly the triple combination therapy elexacaftor-tezacaftor-ivacaftor (Trikafta/Kaftrio), which has transformed CF from a fatal childhood disease into a chronic condition compatible with near-normal life expectancy in many patients. [4]

Key Clinical Messages

The Multi-System Nature of CF

Clinical Pearls

"The Salty Kiss": A historical European folklore reference describes children who taste salty when kissed as being cursed to early death. This observation reflects the elevated sweat chloride that remains the diagnostic gold standard for CF.

The "90-10" Rule: Approximately 90% of CF patients are now eligible for highly effective CFTR modulator therapy, while the remaining 10% with nonsense mutations or rare variants remain without disease-modifying treatment and await gene therapy advances.

Meconium Ileus Diagnostic Yield: While 90% of neonates presenting with meconium ileus have CF, only 15-20% of CF patients present with meconium ileus at birth. [5]

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2. Epidemiology

Global Burden

Cystic fibrosis affects approximately 100,000 individuals worldwide, with the highest prevalence in populations of Northern European ancestry. [1] The incidence varies significantly by ethnicity and geography.

UK Statistics

The UK CF Registry reports approximately 10,800 individuals living with CF in the United Kingdom, with approximately 200 new diagnoses annually. [6] The median age of the UK CF population has increased from 14 years in 1990 to over 20 years currently, reflecting improved survival.

Survival Trends

The prognosis for CF has improved dramatically over the past six decades: [3,7]

The 2019 CF Foundation Patient Registry data demonstrated that individuals born between 2015-2019 have a predicted median survival of 50.6 years. [3] This is expected to increase further with widespread access to elexacaftor-tezacaftor-ivacaftor therapy.

Age at Diagnosis

With universal newborn screening implemented in most developed countries, the median age at diagnosis has decreased substantially: [8]

• Newborn screening detected: 85-90% (first weeks of life)
• Clinical presentation: 10-15% (symptoms before screening result or false-negative screen)
• Late diagnosis: less than 5% (mild phenotypes, atypical presentations)

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3. Genetics and Molecular Biology

The CFTR Gene

The CFTR gene was identified in 1989 through positional cloning, representing a landmark achievement in human genetics. [9] Key characteristics include:

CFTR Protein Structure and Function

The CFTR protein is a member of the ATP-binding cassette (ABC) transporter superfamily and functions as a cAMP-regulated chloride and bicarbonate channel. [10] The protein comprises five domains:

1. Two Membrane-Spanning Domains (MSD1 and MSD2): Form the channel pore
2. Two Nucleotide-Binding Domains (NBD1 and NBD2): Bind and hydrolyse ATP
3. Regulatory (R) Domain: Contains multiple phosphorylation sites for PKA regulation

The CFTR channel performs multiple functions:

• Chloride secretion: Primary function in airway, intestinal, and pancreatic epithelia
• Bicarbonate transport: Critical for pH regulation and mucus fluidity
• Regulation of ENaC: Inhibits epithelial sodium channel activity
• Regulation of other channels: Modulates outwardly rectifying chloride channels

Mutation Classification

Over 2,000 CFTR variants have been identified, with more than 400 confirmed to cause CF. Mutations are classified into six functional classes based on their effect on CFTR protein: [11]

F508

del: The Predominant Mutation

The F508del mutation (deletion of phenylalanine at position 508) accounts for approximately 70% of CF alleles worldwide and up to 90% in Northern European populations. [1,11] This Class II mutation results in:

1. Misfolding: The protein misfolds in the endoplasmic reticulum
2. ER retention: Quality control mechanisms prevent trafficking to plasma membrane
3. Degradation: The protein undergoes proteasomal degradation
4. Minimal surface expression: less than 1% of wild-type levels reach the cell surface

Importantly, F508del causes both trafficking (Class II) and gating (Class III) defects, explaining why triple therapy combining correctors and a potentiator is required for optimal efficacy. [12]

Genotype-Phenotype Correlations

Modifier Genes

Significant phenotypic variability exists among patients with identical CFTR genotypes, attributable to modifier genes: [13]

• TGFB1: Transforming growth factor beta 1 variants influence lung disease severity
• IFRD1: Interferon-related developmental regulator 1 affects neutrophil function
• MBL2: Mannose-binding lectin variants affect infection susceptibility
• EDNRA: Endothelin receptor A variants influence meconium ileus risk
• SLC26A9: Chloride/bicarbonate exchanger modifies lung disease and CFRD risk

Inheritance Patterns and Genetic Counselling

CF follows classic Mendelian autosomal recessive inheritance: [14]

Important Genetic Counselling Points:

• For unaffected siblings of a CF patient: 2/3 probability of being a carrier
• Cascade testing is recommended for first-degree relatives
• Population carrier screening increasingly offered
• Preimplantation genetic diagnosis available for affected families

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4. Pathophysiology

The Airway Surface Liquid Hypothesis

The fundamental pathophysiological mechanism in CF airways relates to dehydration of the airway surface liquid (ASL) layer: [15]

1. Normal Physiology: CFTR secretes chloride (and bicarbonate) into the airway lumen; water follows osmotically; ENaC absorbs sodium with water following
2. CF Defect: Absent/dysfunctional CFTR cannot secrete chloride; ENaC is hyperactive (CFTR normally inhibits ENaC); excessive sodium and water absorption
3. ASL Dehydration: The periciliary layer becomes dehydrated and compressed
4. Ciliary Dysfunction: Cilia cannot beat in the thickened mucus layer
5. Mucociliary Failure: Mucus stasis occurs, trapping bacteria

The Neutrophilic Inflammatory Cascade

CF airways are characterised by a vicious cycle of infection and inflammation: [16]

Defective CFTR → ASL Dehydration → Mucus Stasis
                                      ↓
                            Bacterial Colonisation
                            (S. aureus → P. aeruginosa)
                                      ↓
                          Neutrophil Recruitment
                                      ↓
                    ┌─────────────────┴─────────────────┐
                    ↓                                   ↓
            Oxidative Burst                   Neutrophil Elastase Release
                    ↓                                   ↓
            Host Tissue Damage              Proteolytic Lung Damage
                    ↓                                   ↓
                    └─────────────→ BRONCHIECTASIS ←───┘

Neutrophil-derived products including elastase, DNA, and actin contribute to mucus viscosity, creating a self-perpetuating cycle.

Bicarbonate and Mucus Abnormalities

Beyond chloride, CFTR-mediated bicarbonate secretion is critical for normal mucus properties: [17]

• Normal Mucus: Bicarbonate maintains alkaline pH, allowing mucin granule expansion and proper mucus rheology
• CF Mucus: Reduced bicarbonate leads to acidic pH, dense aggregated mucins, and hyperconcentrated mucus

This explains why even partial CFTR correction may significantly improve mucus properties.

Pancreatic Pathophysiology

The exocrine pancreas is affected early in CF, often prenatally: [18]

1. In Utero: Thick secretions obstruct small pancreatic ducts
2. Autodigestion: Trapped enzymes cause autodigestion of acinar tissue
3. Fibrosis: Progressive replacement with fibrous tissue
4. Insufficiency: By age 1-2 years, 85-90% of CF patients are pancreatic insufficient
5. Islet Damage: Progressive destruction leads to CFRD (40-50% by adulthood)

Hepatobiliary Pathophysiology

CF liver disease (CFLD) affects 5-10% of patients and results from: [19]

1. Bile Inspissation: Defective CFTR in biliary epithelium leads to thick bile
2. Ductular Obstruction: Focal biliary cirrhosis develops
3. Multilobular Cirrhosis: Progressive in some patients
4. Portal Hypertension: May develop independent of synthetic dysfunction

Intestinal Pathophysiology

The intestinal manifestations result from: [20]

• Meconium Ileus: Thick, inspissated meconium obstructs terminal ileum (15% of CF neonates)
• DIOS: Adult equivalent; thick faeces cause ileocaecal obstruction
• Reduced Motility: Altered intestinal transit and dysmotility
• Increased Malignancy Risk: Elevated colorectal cancer risk in CF adults

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5. Clinical Presentation

Neonatal Presentations

Infant and Young Child Presentations

Older Child and Adolescent Presentations

Physical Examination Findings

General Inspection

• Digital clubbing: Universal in advanced disease; absence questions diagnosis
• Cyanosis: In advanced respiratory disease

Respiratory Examination

Gastrointestinal Examination

• Abdominal distension: Malabsorption, DIOS
• Hepatomegaly: CF liver disease
• Splenomegaly: Portal hypertension
• Right iliac fossa mass: DIOS, appendix abscess

Other Systems

• Nasal polyps on rhinoscopy
• Delayed puberty staging
• HPOA: Painful periostitis in wrists/ankles

The "Classical Triad" for Clinical Diagnosis

While newborn screening has largely superseded clinical diagnosis, the historical triad remains relevant for late presentations:

1. Chronic suppurative lung disease
2. Exocrine pancreatic insufficiency
3. Elevated sweat chloride

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6. Diagnosis

Newborn Screening

Most developed countries have implemented universal newborn screening for CF, which has significantly improved outcomes through early detection and treatment. [8,21]

UK Screening Protocol (Example)

Day 5-8: Heel prick blood spot
           ↓
    Immunoreactive Trypsinogen (IRT) Measurement
           ↓
    ┌──────┴──────┐
    ↓             ↓
IRT Normal    IRT Elevated (> 99.5th centile)
    ↓             ↓
 STOP        CFTR Mutation Analysis
                  ↓
         ┌────────┴────────┐
         ↓                 ↓
    2 Mutations       0-1 Mutations
         ↓                 ↓
    CF Confirmed      Repeat IRT at Day 21-28
                          ↓
                    ┌─────┴─────┐
                    ↓           ↓
              IRT Normal    IRT Elevated
                    ↓           ↓
                  STOP      Sweat Test

IRT Biology

• Source: Immunoreactive trypsinogen leaks from blocked pancreatic ducts into blood
• Timing: Elevated in first weeks of life in CF; falls to low/normal with pancreatic destruction
• Sensitivity: 85-90% for CF detection
• False Positives: Prematurity, perinatal stress, carrier status

Sweat Test (Diagnostic Gold Standard)

The quantitative pilocarpine iontophoresis sweat test remains the cornerstone of CF diagnosis. [22]

Methodology

1. Stimulation: Pilocarpine applied to forearm/thigh with iontophoresis
2. Collection: Sweat collected onto gauze or Macroduct coil for minimum 75 mg or 15 μL
3. Analysis: Chloride concentration measured by coulometry

Interpretation

Quality Control Requirements

• Minimum sweat quantity: 75 mg (Gibson-Cooke) or 15 μL (Macroduct)
• Two positive tests recommended for confirmation
• Performed at accredited CF centre
• Avoid false positives: eczema over collection site, dehydration, malnutrition

Causes of False Results

Genetic Testing

Genetic confirmation is essential following positive sweat test and for family screening: [14]

Testing Strategies

Diagnostic Criteria (CFF/ECFS Consensus)

CF is diagnosed when:

1. Sweat chloride ≥60 mmol/L, OR
2. Two disease-causing CFTR mutations in trans, AND
3. Clinical features consistent with CF or positive newborn screen

CFTR-Related Disorder (CFTR-RD):

• Sweat chloride 30-59 mmol/L or one disease-causing mutation
• Single organ manifestation (CBAVD, pancreatitis, bronchiectasis)
• Does not meet full CF diagnostic criteria

Adjunctive Diagnostic Tests

Nasal Potential Difference (NPD)

• Measures chloride and sodium transport across nasal epithelium
• CF pattern: More negative baseline, absent response to chloride-free solution and isoproterenol, exaggerated amiloride response
• Available at specialist centres only

Intestinal Current Measurements (ICM)

• Rectal biopsy assessed in Ussing chamber
• Gold standard for CFTR function assessment
• Limited availability

Faecal Elastase-1

• Screens for pancreatic exocrine insufficiency
• FE-1 less than 200 μg/g: Pancreatic insufficiency likely
• Does not diagnose CF but supports clinical picture

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7. Multi-System Management Overview

Principles of CF Care

CF management requires a coordinated multidisciplinary team (MDT) approach delivered through specialist CF centres, as mandated by national standards. [23]

The CF MDT

Care Frequency

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8. CFTR Modulator Therapy

The Therapeutic Revolution

CFTR modulators represent a paradigm shift in CF treatment, addressing the underlying molecular defect rather than symptoms. [4,12,24]

Types of Modulators

Available Modulator Therapies

Ivacaftor (Kalydeco) - 2012

Clinical Efficacy (G551D patients):

• FEV1 improvement: +10-11% absolute
• Pulmonary exacerbations: 55% reduction
• Weight gain: +2.7 kg
• Sweat chloride: -48 mmol/L

Lumacaftor-Ivacaftor (Orkambi) - 2015

Clinical Efficacy:

• FEV1 improvement: +2.6-4% absolute
• Pulmonary exacerbations: 30-39% reduction
• Significant drug-drug interactions (CYP3A4 induction)

Tezacaftor-Ivacaftor (Symdeko/Symkevi) - 2018

Elexacaftor-Tezacaftor-Ivacaftor (Trikafta/Kaftrio) - 2019

Landmark Clinical Efficacy (F508del heterozygotes): [4]

Real-World Effects:

• Dramatic reduction in sputum production
• Improved exercise tolerance
• Reduced need for IV antibiotics
• Weight gain (dietary adjustment required)
• Improved quality of life
• Sinus symptom improvement
• CFRD stabilisation in some patients

Modulator Side Effects and Monitoring

Drug Interactions

Ivacaftor is metabolised by CYP3A4; significant interactions exist:

The "Unmodulatable" 10%

Approximately 10% of CF patients have mutations not responsive to current modulators (primarily Class I nonsense mutations): [26]

Current Status:

• No approved modulator therapy
• Poorer prognosis than modulator-eligible patients
• Priority population for gene therapy research

Investigational Approaches:

• Nonsense suppression (ELX-02, ataluren)
• Gene therapy (viral vectors, lipid nanoparticles, mRNA)
• Gene editing (CRISPR-Cas9)

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9. Respiratory Management

Airway Clearance Techniques (ACT)

Airway clearance is the cornerstone of CF respiratory care, required twice daily for most patients. [27]

Technique Selection by Age

Active Cycle of Breathing Technique (ACBT)

The most widely taught and evidence-based technique:

1. Breathing Control: Relaxed tidal breathing, emphasising diaphragmatic breathing
2. Thoracic Expansion Exercises: Deep inspiration to total lung capacity, 3-second hold, passive expiration
3. Forced Expiration Technique (Huffing): Medium to low lung volume huffs to mobilise secretions, followed by coughing

Positive Expiratory Pressure (PEP)

Exercise as Airway Clearance

• Benefit: Increases ventilation, mobilises secretions, maintains fitness
• Evidence: 30 minutes of moderate-intensity exercise can substitute for one ACT session
• Recommendation: Encourage regular physical activity; does not fully replace ACT in most patients

Mucolytic Therapy

Dornase Alfa (rhDNase, Pulmozyme)

Hypertonic Saline (7%)

Mannitol (Bronchitol)

• Dry powder inhaler; alternative to nebulised hypertonic saline
• Similar osmotic mechanism
• Requires bronchial challenge test before initiation

Anti-Inflammatory Therapy

Azithromycin

Corticosteroids

• Inhaled: No routine role; may benefit ABPA or significant bronchospasm
• Oral: Reserved for ABPA treatment; avoid long-term use due to side effects (osteoporosis, diabetes, growth suppression)

Inhaled Antibiotic Therapy

Chronic suppressive therapy for patients with persistent Pseudomonas aeruginosa infection: [31]

Systemic Antibiotics for Exacerbations

Definition of Pulmonary Exacerbation

Treatment Approach

Common IV Antibiotic Combinations

Pseudomonas aeruginosa: Eradication and Chronic Management

First Isolation Eradication Protocol

Goal: Prevent transition to chronic infection

Standard Protocol:

• Oral ciprofloxacin (15-20 mg/kg BD, max 750 mg BD) for 3 months
• PLUS nebulised colistin (1-2 MU BD) for 3 months
• Repeat sputum cultures monthly

Alternative (if ciprofloxacin resistant):

• IV anti-pseudomonal antibiotics for 2-3 weeks
• Plus nebulised antibiotics for 3 months

Success Definition: Three consecutive negative cultures over 6-12 months

Chronic Pseudomonas Infection

Defined as: Positive cultures in ≥50% of samples over preceding 12 months (Leeds criteria)

Management:

1. Long-term inhaled anti-pseudomonal antibiotics (continuous or alternating)
2. Azithromycin maintenance
3. Aggressive treatment of exacerbations
4. Regular sputum surveillance
5. Consideration for eradication attempt if new strain

Burkholderia cepacia Complex

Critical pathogen with major implications for prognosis and transplant eligibility: [32]

Non-Tuberculous Mycobacteria (NTM)

Emerging problem in CF, particularly M. abscessus complex: [33]

NTM may preclude lung transplantation at some centres.

Complications: Haemoptysis

Complications: Pneumothorax

• Incidence: 3-4% per year in advanced disease
• Presentation: Sudden pleuritic pain, breathlessness, reduced air entry
• Diagnosis: Chest X-ray (erect if possible)
• Management: Small (less than 2 cm) may observe; larger requires chest drain
• Recurrence Prevention: Pleurodesis (chemical or surgical) after first episode
• Transplant Implications: Previous pleurodesis complicates surgery but not absolute contraindication

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10. Gastrointestinal and Nutritional Management

Pancreatic Enzyme Replacement Therapy (PERT)

Approximately 85-90% of CF patients require PERT for pancreatic insufficiency. [18]

Pancreatin Products

Dosing Principles

Maximum Dose: 10,000 lipase units/kg/day (to avoid fibrosing colonopathy)

Administration

1. Capsules taken at START of meal/snack containing fat
2. If prolonged meal, give half at start, half during
3. For infants: Open capsule, mix granules with small amount of fruit puree, give with spoon
4. Never crush or chew enteric-coated granules (mouth ulceration, enzyme inactivation)

Signs of Inadequate Dosing

• Steatorrhoea (pale, bulky, offensive stools)
• Abdominal pain, bloating
• Poor weight gain despite adequate intake
• Excessive flatulence

Fibrosing Colonopathy

Rare but serious complication of high-dose PERT:

• Strictures of ascending colon
• Associated with > 6,000 units lipase/kg/meal
• Presents with abdominal pain, constipation, obstruction
• Prevention: Adhere to maximum dose guidelines

Nutritional Requirements

CF patients have increased energy requirements due to chronic infection/inflammation, malabsorption, and increased work of breathing: [34]

Target BMI:

• Children: ≥50th percentile for age/sex
• Adults: ≥22 kg/m² (females), ≥23 kg/m² (males)

Nutritional Interventions Ladder

1. Dietary Counselling: High-calorie, high-fat diet; regular meals and snacks
2. Oral Supplements: High-energy drinks (Fortisip, Ensure Plus)
3. Nasogastric Feeding: Short-term or overnight; rarely long-term
4. Gastrostomy (PEG/RIG): For chronic nutritional failure; enables overnight feeds
5. Parenteral Nutrition: Rarely required; short gut, failed enteral

Fat-Soluble Vitamin Supplementation

All pancreatic-insufficient patients require fat-soluble vitamin supplementation:

Common preparations: Dalivit, ADEK, Vitabiotics CF supplements

Salt Supplementation

CF patients lose excess sodium in sweat and are at risk of hyponatraemic dehydration: [35]

Pseudo-Bartter Syndrome: Severe hyponatraemic, hypokalaemic, hypochloraemic metabolic alkalosis presenting with lethargy, anorexia, failure to thrive

Distal Intestinal Obstruction Syndrome (DIOS)

Management:

1. Incomplete DIOS: Oral Gastrografin (100 mL) or Klean-Prep; increase fluids
2. Complete DIOS: IV fluids, NG tube if vomiting, Gastrografin enema or oral
3. Surgery: Last resort if perforation, peritonitis, or failed medical management

CF-Related Liver Disease (CFLD)

Affects 5-10% of patients with clinically significant disease:

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11. CF-Related Diabetes (CFRD)

CFRD is the most common extrapulmonary complication of CF. [36]

Epidemiology

Pathophysiology

CFRD has features of both Type 1 and Type 2 diabetes:

• Insulin Deficiency: Progressive destruction of islets by fibrosis
• Insulin Resistance: Acute/chronic infection, steroids, liver disease
• Preserved Glucagon: Unlike Type 1, glucagon response intact
• Variable Course: May worsen during exacerbations, improve with treatment

Screening and Diagnosis

Categories:

• CFRD with fasting hyperglycaemia: Fasting glucose ≥7.0 mmol/L
• CFRD without fasting hyperglycaemia: Fasting normal but 2-hour ≥11.1 mmol/L
• Impaired glucose tolerance: 2-hour 7.8-11.0 mmol/L

Management

Key Difference from Type 2 DM: Insulin, not lifestyle modification, is first-line therapy

Microvascular Complications

Long-standing CFRD can lead to:

• Retinopathy: Annual dilated fundoscopy from 5 years after diagnosis
• Nephropathy: Annual urinary ACR
• Neuropathy: Rare, but screen if symptomatic

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12. Annual Review Protocol

Comprehensive annual assessment is mandated by CF standards of care. [23]

Annual Review Components

Lung Function Monitoring

Severity Grading by FEV1:

Imaging

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13. Special Populations

Transition to Adult Care

A structured transition process is essential, typically beginning at age 12-14 with transfer at 16-18 years: [37]

Key Topics for Transition:

• Self-management of medications and physiotherapy
• Fertility and contraception
• Career planning and disclosure
• Alcohol and recreational drugs
• Adult healthcare navigation

Fertility and Reproduction

Males

Females

Pregnancy in CF

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14. Psychosocial Aspects

Mental Health Burden

CF patients and caregivers have elevated rates of depression and anxiety: [38]

Contributing Factors:

• Daily treatment burden (2-4 hours/day)
• Unpredictable exacerbations
• Fertility concerns
• Mortality awareness
• Social isolation (infection control)

Treatment Burden

Daily CF treatment regimen (pre-modulator era):

CFTR modulators have reduced some of this burden, but adherence remains challenging.

Adherence

Adherence to CF treatments is often suboptimal, particularly in adolescence:

• Physiotherapy: 40-60% full adherence
• Nebulised medications: 50-70%
• PERT: 70-80%
• CFTR modulators: 80-90%

Strategies to Improve Adherence:

• Simplify regimens where possible
• Motivational interviewing
• Digital health tools and reminders
• Psychology support
• Peer support programmes

Infection Control and Social Isolation

The "5-Metre Rule": CF patients should maintain ≥2 metres distance from other CF patients (some centres 3-5 metres) to prevent cross-infection with Pseudomonas and Burkholderia.

Implications:

• CF camps/events require careful planning
• Online CF communities important for peer support
• Hospital segregation policies

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15. Emerging Therapies and Future Directions

Gene Therapy

The ultimate goal remains correcting the underlying genetic defect: [26]

Gene Editing

CRISPR-Cas9 and base editing approaches are under investigation for permanent correction:

• Potential for single treatment cure
• Challenges: Delivery to sufficient cells, off-target effects
• Timeline: Early research phase; clinical trials years away

Amplifiers and Next-Generation Modulators

• Amplifiers: Increase amount of CFTR protein available for correction
• Next-gen Correctors: More effective for rare mutations
• Combination Strategies: Triple + amplifier regimens

Lung Transplantation Advances

• Extended criteria donors
• Ex vivo lung perfusion (EVLP)
• Anti-rejection advances
• Post-transplant outcomes improving

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16. Prognosis

Survival

The prognosis for CF has improved dramatically: [3,7]

Prognostic Factors

Impact of CFTR Modulators on Prognosis

Modelling studies suggest that individuals starting elexacaftor-tezacaftor-ivacaftor at young ages may achieve near-normal life expectancy, though long-term real-world data are awaited.

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17. Examination Focus

Common MRCPCH Questions

1. "Describe the newborn screening pathway for CF and its limitations"
2. "A 3-month-old presents with failure to thrive and recurrent chest infections - how would you investigate?"
3. "Explain the mechanism of action of CFTR modulators"
4. "How would you manage first isolation of Pseudomonas aeruginosa?"
5. "What are the indications for lung transplantation in CF?"

Viva Points

Opening Statement: "Cystic fibrosis is the most common life-limiting autosomal recessive disorder in Caucasian populations, affecting approximately 1 in 2,500 births. It is caused by mutations in the CFTR gene, leading to defective chloride channel function and multisystem disease predominantly affecting the respiratory and gastrointestinal systems."

Key Facts to Quote:

• F508del accounts for ~70% of alleles worldwide
• Sweat chloride ≥60 mmol/L is diagnostic
• 85-90% have pancreatic insufficiency
• Triple therapy (Kaftrio/Trikafta) improves FEV1 by ~14%
• Current median survival exceeds 50 years

Common Mistakes (What Fails Candidates)

• Stating HbA1c is reliable for CFRD monitoring (it is NOT - use OGTT)
• Recommending calorie restriction in CFRD
• Forgetting the maximum PERT dose (10,000 units/kg/day)
• Not mentioning infection control between CF patients
• Overlooking the need for pre-bronchodilator before hypertonic saline

Model Answer: "How would you manage a pulmonary exacerbation?"

"I would assess the patient clinically, looking for increased cough, sputum volume and purulence, dyspnoea, and reduced exercise tolerance. I would measure oxygen saturations, perform spirometry to document any FEV1 decline from baseline, and obtain sputum for culture. My management would depend on severity. For a mild exacerbation, I might use oral antibiotics such as ciprofloxacin combined with another agent based on previous sensitivities, for 14 days. For moderate-to-severe exacerbations, I would arrange IV antibiotics, typically two anti-pseudomonal agents such as tobramycin and ceftazidime, for 14-21 days. This could be delivered at home via a port-a-cath if established, or in hospital. I would intensify physiotherapy and ensure adequate nutrition. I would review the response with repeat spirometry and adjust the plan accordingly."

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18. Key Guidelines

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Topic: Cystic Fibrosis in Children (782/1071) Senior Editor: Dr. N. Goyal (Paediatrics) Guideline Verification: NICE NG78 / ECFS 2018 / CF Trust Standards

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