Key learning points
- Cystic fibrosis is a genetic life-shortening condition that affects many organs in the body
- The effects on the lower airway are the main feature of the condition, with thickened ductal secretions resulting in a cycle of increased airway infections and inflammation, leading to progressive airways damage
- FEV1 is used to inform clinical decisions relating to airway infection, inflammation and mucus, and responses to treatment, as well as to monitor disease and severity
- Multidisciplinary, specialist care is essential in the management of patients with cystic fibrosis
- Novel therapies have shown improvements in lung function and a reduced frequency of pulmonary exacerbations
Cystic fibrosis (CF) is a multisystem, monogenic disease predominantly affecting Caucasian people. It is caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene which encodes for the CFTR protein, an epithelial ion channel located at the apical surface of the cell membrane of specific organ tissues: sweat glands, conducting airway, pancreatic and biliary ducts, intestinal mucosa and the male vas deferens. Absent or net reduction in quantity or function of the CFTR protein produces features of abnormal ion transport and leads to the clinical syndrome within these organ-sites, which is typified by thickened luminal secretions. Treatments to date have considerably improved morbidity and increased life expectancy, but despite an increasing emergence of new treatments and therapies, CF remains a life-shortening condition.
CF is inherited in an autosomal recessive manner and thus requires both parents to pass one mutated gene to their affected child; the parents, being heterozygotes (‘carriers’) for CFTR, are unaffected by the disease. The incidence and prevalence of CF varies globally. Approximately one in 19 people in Ireland are carriers of a faulty CFTR gene, and it is estimated that the prevalence of CF in Ireland is one in 1,300. Data from the 2018 Cystic Fibrosis Registry of Ireland (CFRI) complied by Cystic Fibrosis Ireland records over 1,300 patients currently living with CF, with a current median age of survival as 33 years.1,2 The median predicted survival is, however, increasing annually, with epidemiological modelling predicting that individuals born in the year 2000 will have a median survival of >50 years old, and with modern therapies aiming to correct the underlying cellular defect, exponential increases in life expectancy are a realistic potential.3
It is the consequences in the lower airway that is the predominant feature of the condition, leading to premature death in approximately 80% of patients.4 Thickened ductal secretions result in a perpetuating cycle of increased airway infections and inflammation, leading to progressive airways damage. This process may be extrapolated to explain the extra-pulmonary manifestations of the disease with end-organ failure. The clinical features seen in people living with CF are summarised in Table 1.
Measurements of lung function, in particular the forced expiratory volume in one second (FEV1), are important clinical tools in the care of CF patients. They inform clinical decisions relating to airway infection, inflammation and mucus, and responses to treatment; and are used longitudinally to monitor disease and severity.5
Table 1. Organ- and system-specific clinical features in cystic fibrosis
|Organ affected||Clinical features|
|Lower airway||Increased, thickened mucus production
Acute and chronic airway infection especially with Pseudomonas aeruginosa, Staphylococcus aureus and Haemophilus influenzae
Atypical Mycobacterium infection
Allergic bronchopulmonary aspergillosis
|Pancreas||Pancreatic insufficiency (exocrine failure) leading to malabsorption and vitamin deficiency states
CF-related diabetes (endocrine failure)
|Gastrointestinal tract||Gastro-oesophageal reflux
Distal intestinal obstruction syndrome
Increased risk of GI tract malignancy
|Hepatobiliary system||CF-related liver disease (encompassing cholestatic cirrhosis and liver failure)
Biliary stasis and cholelithiasis
|Genitourinary system||Male infertility (congenital bilateral absence of the vas deferens)
Reduced female fertility (thickened cervical mucus)
Delayed puberty (probably secondary to nutritional, inflammatory and/or drug effects rather than primary)
|Skin||Raised sweat chloride (diagnostic gold standard)
Electrolyte depletion (pseudo-Bartter’s syndrome)
|Bones||Low bone mineral density and osteoporosis
Since 2011, Ireland has implemented universal newborn screening for CF by the measurement of immune-reactive trypsinogen in the serum following a heel-prick test. Positive results are next assessed for common CFTR mutations, with diagnosis still requiring a sweat test for confirmation.6,7 Patients with mild or ‘atypical’ CF disease may present in later life with at least one organ-specific CF symptom, most commonly bronchiectasis or infertility. Such patients should be evaluated in a specialist bronchiectasis or CF service by CFTR genetic analysis and functional CFTR testing.8
Management of cystic fibrosis
Multidisciplinary, specialist care is essential in the management of patients with CF. To date, Ireland has 13 CF centres.9 The Health Service Executive (HSE) National Clinical Programme for Cystic Fibrosis (NCPCF) recently launched ‘Cystic Fibrosis – A Model of Care for Ireland’ outlining how the care of people with cystic fibrosis should be organised. One of the key recommendations is that people with cystic fibrosis must receive their CF care from and have regular follow-up by a designated cystic fibrosis centre, each with multidisciplinary teams (CF dedicated physicians, specialist nurses, physiotherapists, dietitians, pharmacists, psychologists and social workers), and supported by specialty services (including diabetes, gastroenterology, hepatology and ENT).10
Until recently, CF management has concentrated on the downstream effects of CF. The treatment of chronic airways disease centres around airway clearance by physiotherapy, aided by nebulised or inhaled mucolytic agents, and treatment of airway infection and inflammation. Acute and chronic pulmonary infection with S. aureus (methicillin sensitive and resistant), Pseudomonas aeruginosa and non-tuberculous Mycobacteria are common in CF, alongside other emerging organisms. Treatment for an acute pulmonary exacerbation is managed with oral or intravenous antibiotics targeted at the likely organism; long-term nebulised, inhaled or oral antibiotics are prescribed for established, chronic infection.
In the last decade, novel therapies have emerged that correct or potentiate the CFTR protein, demonstrating improvements in lung function and a reduced frequency of pulmonary exacerbations. Such drugs are CFTR mutation-specific and costly and are currently available as part of the HSE’s CF reimbursement agreement with the manufacturer. The CFTR potentiator ivacaftor is approved for clinical use in eligible patients based on their mutation genotype (17%).1 Two further licensed therapies (a combination of a corrector and potentiator) are available to eligible patients (aged >12 years) – these are lumacaftor–ivacaftor11 and tezacaftor–ivacaftor.12 Following an announcement reporting a positive trial outcome, a new triple combination (elexacaftor, tezacaftor and ivacaftor) will also be added to the reimbursement agreement.13
Optimisation of weight by the oral replacement of pancreatic (digestive) enzymes, and by appropriate vitamin and mineral supplementation is key, along with the management of CF-related diabetes. Bilateral lung transplantation may be considered as a treatment for end-stage lung disease. In 2018, 8 bilateral lung transplants in patients with CF were carried out in Ireland.1
Future of CF care
The importance of providing personalised care is becoming ever more important as novel therapies develop and target the disease at the cellular level. Next-generation CFTR correctors, including triple combination therapies, are emerging along the CF therapeutics pipeline.14 Genetic therapies, CFTR gene therapy and genome editing, both correcting the underlying genetic defect, remain the holy grail in CF treatment. To date, CFTR gene therapy has proven concept but its efficacy remains to be established. It seems likely that in an era of CFTR modulator therapy, the life expectancy of patients with CF will continue to rise over and above previous modelling.
Dr Michael Waller, consultant in cystic fibrosis and respiratory medicine; Dr Caroline Elston, consultant in respiratory medicine and adult cystic fibrosis, Department of Adult Cystic Fibrosis, King’s College Hospital, London
This project was initiated and funded by Teva Respiratory. Teva have had no influence over content. Topics and content have been selected and written by independent experts.