# Cystic Fibrosis Across the Lifespan

## Overview
Cystic fibrosis (CF) is an autosomal recessive multisystem disease caused by mutations in the CFTR gene encoding the cystic fibrosis transmembrane conductance regulator chloride channel. Once a fatal childhood disease, the median predicted survival now exceeds 50 years due to CFTR modulator therapies, and the majority of CF patients are now adults.

## Genetics and Pathophysiology
CFTR gene located on chromosome 7q31.2. Over 2,000 mutations identified; classified into 6 functional classes. F508del (Class II -- protein misfolding) is the most common mutation, present in ~70% of CF alleles. Defective chloride and bicarbonate transport leads to thick, dehydrated secretions. Affected organ systems: lungs, pancreas, liver, intestines, sweat glands, vas deferens. Sweat chloride elevation is the basis of the diagnostic sweat test.

### CFTR Mutation Classes

| Class | Defect | Example | Modulator Responsive |
|-------|--------|---------|---------------------|
| I | No protein production (nonsense, splice site) | G542X | Not currently |
| II | Protein misfolding and degradation | F508del | Yes (Trikafta) |
| III | Gating defect (channel does not open) | G551D | Yes (Ivacaftor) |
| IV | Conductance defect (reduced chloride flow) | R117H | Yes (Ivacaftor) |
| V | Reduced protein quantity | — | Variable |
| VI | Decreased protein stability | — | Variable |

## Diagnosis
Newborn screening: immunoreactive trypsinogen (IRT) followed by CFTR mutation analysis. Confirmatory sweat chloride test: >60 mmol/L is diagnostic, 30-59 is intermediate. CFTR mutation panel or gene sequencing. Nasal potential difference or intestinal current measurements for borderline cases. CFTR-related metabolic syndrome (CRMS/CFSPID): infants with positive screen but inconclusive diagnosis.

## Pulmonary Disease

### Pediatric Lung Disease
Progressive bronchiectasis and chronic infection begin in infancy. Early pathogens: Staphylococcus aureus, Haemophilus influenzae. Pseudomonas aeruginosa: acquisition in childhood predicts worse outcomes. Aggressive eradication protocols for new Pseudomonas. Airway clearance techniques (chest physiotherapy, vest, PEP devices) Mucolytics: dornase alfa (Pulmozyme), hypertonic saline. Chronic azithromycin for anti-inflammatory effect.

### Adult Lung Disease
Progressive decline in FEV1 (historically 1-2% per year pre-modulators) Chronic Pseudomonas infection in ~60% of adults. Burkholderia cepacia complex: associated with rapid decline, poor transplant outcomes. Nontuberculous mycobacteria (NTM): increasing prevalence, complex treatment. Allergic bronchopulmonary aspergillosis (ABPA) Massive hemoptysis: bronchial artery embolization. Pneumothorax: high recurrence rate. Lung transplantation: bilateral sequential lung transplant is definitive therapy for end-stage CF lung disease.

## CFTR Modulator Therapies

### Elexacaftor/Tezacaftor/Ivacaftor (Trikafta)
Approved for ages 2+ with at least one F508del mutation; Triple combination: corrector + corrector + potentiator; FEV1 improvement: ~14 percentage points; Sweat chloride reduction: ~40 mmol/L; Dramatic reduction in pulmonary exacerbations, hospitalizations; Improved BMI, quality of life, and potentially fertility; Has transformed the CF landscape since FDA approval in 2019.

### Other Modulators

| Drug (Brand) | Mechanism | Eligible Genotype | Age Approval |
|-------------|-----------|-------------------|-------------|
| Ivacaftor (Kalydeco) | Potentiator | Gating mutations (G551D) | 4 months+ |
| Lumacaftor/ivacaftor (Orkambi) | Corrector + potentiator | F508del homozygotes | 1 year+ |
| Tezacaftor/ivacaftor (Symdeko) | Corrector + potentiator | F508del | 6 years+ |
| Elexacaftor/tezacaftor/ivacaftor (Trikafta) | 2 correctors + potentiator | At least one F508del | 2 years+ |

Not all mutations are modulator-responsive (~10% of patients have no eligible mutation)

### Controversy: Impact on Airway Clearance
Do patients on highly effective modulator therapy (HEMT) still need aggressive airway clearance? Emerging data suggest some patients can reduce treatments but no consensus guidelines exist. Risk of complacency and treatment reduction leading to future decline. Long-term studies ongoing.

## Extrapulmonary Manifestations

### Pancreatic Disease
Exocrine pancreatic insufficiency in ~85% of CF patients. Pancreatic enzyme replacement therapy (PERT) with meals and snacks. Fat-soluble vitamin supplementation (A, D, E, K) CF-related diabetes (CFRD): affects ~20% of adolescents and ~50% of adults. Distinct pathophysiology: primarily insulin deficiency from pancreatic fibrosis. Insulin is the only recommended treatment (not metformin or oral agents) Annual screening with OGTT starting at age 10. A1c is unreliable due to altered red cell turnover; use CGM data.

### Hepatobiliary Disease
CF-related liver disease (CFLD): focal biliary cirrhosis progressing to multilobular cirrhosis. Portal hypertension, variceal bleeding; Ursodeoxycholic acid commonly used though evidence is limited; Liver transplantation for end-stage liver disease; HEMT may slow progression of liver disease.

### GI Complications
Meconium ileus in neonates (10-15%); Distal intestinal obstruction syndrome (DIOS) in older patients; GERD: very common, worsens lung disease; Small bowel bacterial overgrowth; Increased risk of GI malignancies (colon cancer screening recommended starting age 40 in CF).

### Bone Disease
CF-related bone disease: osteopenia and osteoporosis. Multifactorial: malabsorption, chronic inflammation, glucocorticoid use, reduced physical activity. DEXA scanning starting at age 18 (or earlier if risk factors) Vitamin D optimization, weight-bearing exercise, bisphosphonates if indicated.

### Reproductive Health
Males: >95% infertile due to congenital bilateral absence of vas deferens (CBAVD) Sperm retrieval and IVF are options. HEMT may improve fertility in some females (thinner cervical mucus) Increased unplanned pregnancies reported since Trikafta. Pregnancy in CF: generally well-tolerated if FEV1 >50% predicted. Genetic counseling: all partners should be offered CFTR carrier testing.

### Mental Health
Depression and anxiety prevalence 2-3x general population; Annual screening recommended (PHQ-9, GAD-7); Treatment burden contributes to mental health challenges; HEMT has improved quality of life but not eliminated mental health burden.

## Transition and Adult CF Care
CF Foundation accredited care centers with multidisciplinary teams; Transition from pediatric to adult CF center typically at age 18-21; Adult CF teams must manage an aging population with new challenges:; Cardiovascular disease; Metabolic syndrome and obesity (new phenomenon in HEMT era); Cancer screening; Pregnancy planning; Aging-related comorbidities.

## Infection Control
CF patients should not be in close proximity to other CF patients (cross-infection risk) Burkholderia cepacia complex and MRSA are transmissible between CF patients. Strict infection control in clinics: separate rooms, temporal separation, masks.

<image>A medical illustration showing the CFTR protein embedded in an airway epithelial cell membrane. The left panel shows normal CFTR function with chloride and bicarbonate transport maintaining thin, hydrated airway surface liquid. The right panel shows defective CFTR (F508del) with thick, dehydrated mucus plugging the airway, trapped bacteria (Pseudomonas shown in green), and neutrophilic inflammation. Below, a third panel shows the mechanism of Trikafta: elexacaftor and tezacaftor correcting protein folding, and ivacaftor holding the channel open, restoring partial chloride transport.</image>

<image>A human body diagram showing the multisystem manifestations of cystic fibrosis across the lifespan. The lungs show progressive bronchiectasis, the sinuses show chronic rhinosinusitis with polyps, the pancreas shows fibrosis with exocrine insufficiency and CFRD, the liver shows focal biliary cirrhosis, the intestines show DIOS, the bones show osteoporosis, and the reproductive organs show CBAVD in males. Age-specific annotations indicate when each complication typically manifests.</image>

<image>A graph illustration showing the dramatic improvement in CF median predicted survival over time from 1960 (approximately 10 years) to 2025 (approximately 55 years). Key milestones are marked on the timeline: introduction of pancreatic enzymes, chest physiotherapy, tobramycin nebulization, dornase alfa, ivacaftor, and elexacaftor/tezacaftor/ivacaftor (Trikafta). The slope steepens markedly after the introduction of CFTR modulators.</image>

<image>A clinical decision flowchart for CF-related diabetes screening and management. Starting with annual OGTT at age 10, branching to normal glucose tolerance, impaired glucose tolerance (with monitoring plan), and CFRD diagnosis. The CFRD branch shows insulin initiation, CGM monitoring, and follow-up targets. A note indicates that A1c underestimates glycemia in CF and should not be used alone for monitoring.</image>

## Clinical Pearls
More than half of all CF patients are now adults -- internists and Med-Peds physicians must be comfortable managing this population. Trikafta (elexacaftor/tezacaftor/ivacaftor) is the most transformative therapy in CF history, eligible for ~90% of CF patients. CFRD is not type 1 or type 2 diabetes -- it requires insulin, and A1c is unreliable; use CGM or OGTT for monitoring. CF patients should never be in the same exam room or waiting area as other CF patients due to cross-infection risk. Male infertility (CBAVD) is nearly universal but fertility can be achieved with sperm retrieval and IVF. Unplanned pregnancies are increasing in the HEMT era due to improved cervical mucus -- counsel all reproductive-age women. Lung transplant remains the definitive therapy for end-stage CF lung disease; refer when FEV1 <30% predicted or rapid decline. Colon cancer screening should begin at age 40 in CF (earlier than general population) due to elevated risk. "Highly effective modulator therapy" does not mean patients can stop all other treatments -- airway clearance, PERT, and vitamin supplementation remain important.

## References
- Middleton PG, Mall MA, Drevinek P, et al. Elexacaftor-tezacaftor-ivacaftor for cystic fibrosis with a single Phe508del allele. N Engl J Med. 2019;381(19):1809-1819.
- Cystic Fibrosis Foundation Patient Registry Annual Data Report. 2022.
- Flume PA, Mogayzel PJ Jr, Robinson KA, et al. Cystic fibrosis pulmonary guidelines: treatment of pulmonary exacerbations. Am J Respir Crit Care Med. 2009;180(9):802-808.
- Moran A, Brunzell C, Cohen RC, et al. Clinical care guidelines for cystic fibrosis-related diabetes. Diabetes Care. 2010;33(12):2697-2708.
- Shteinberg M, Haq IJ, Polineni D, Davies JC. Cystic fibrosis. Lancet. 2021;397(10290):2195-2211.