Cystic Fibrosis — Advanced CFTR Modulator Therapy (Elexacaftor/Tezacaftor/Ivacaftor and Beyond)

Cystic fibrosis (CF) is an autosomal recessive multisystem disease caused by biallelic mutations in CFTR (Cystic Fibrosis Transmembrane Conductance Regulator) gene on chromosome 7q31.2, encoding cAMP-regulated chloride channel expressed in epithelial cells of multiple organs. Worldwide most common in Northern European populations (carrier frequency 1:25, disease frequency 1:2,500–3,500 live births), more rare in Asian and African populations. >2,000 CFTR mutations identified, classified into six functional classes by molecular defect: Class I (no protein production — nonsense, frameshift, splice mutations like W1282X, G542X, R553X), Class II (protein misfolding and ER retention with abnormal trafficking — F508del is most common globally, present in 70 percent of CF alleles, ΔF508 deletion of phenylalanine 508), Class III (gating defect — channel reaches surface but doesn't open properly, e.g., G551D, S549N, G178R), Class IV (reduced channel conductance — R117H, R334W), Class V (splicing defect with reduced normal CFTR — e.g., 3849+10kbC>T), Class VI (reduced surface stability — c.120del23, 4326delTC).

CFTR dysfunction causes defective chloride and bicarbonate transport across epithelial surfaces with secondary sodium hyperabsorption, resulting in dehydrated thickened mucus on airway and other epithelial surfaces. Multisystem manifestations: (1) Lung — chronic airway obstruction, recurrent infection (Staphylococcus aureus, Pseudomonas aeruginosa most prominent, Burkholderia cepacia complex highly virulent, NTM), bronchiectasis, progressive lung function decline, respiratory failure (former leading cause of death); (2) Pancreas — exocrine pancreatic insufficiency in 90 percent (steatorrhea, fat-soluble vitamin deficiencies, malnutrition); (3) CF-related diabetes (CFRD) — 50 percent by age 30, 20 percent by age 30 with insulin requirement; (4) CF liver disease (CFLD) — 5–10 percent develop cirrhosis with portal hypertension; (5) Sinus disease (chronic rhinosinusitis with polyps); (6) GI — meconium ileus in newborns, distal intestinal obstruction syndrome (DIOS) in older patients, GERD; (7) Reproductive — male infertility from CBAVD (congenital bilateral absence of vas deferens) in 98 percent; female reduced fertility; (8) Sweat — elevated sweat chloride is diagnostic >60 mEq/L (Gibson-Cooke pilocarpine iontophoresis sweat test).

Diagnosis: newborn screening with elevated immunoreactive trypsinogen (IRT) followed by CFTR mutation panel and confirmation with sweat chloride testing; classical clinical diagnosis with CF symptoms plus sweat chloride >60 mEq/L on two separate tests (intermediate 30–60 mEq/L requires further workup); CFTR genotyping for mutation identification (essential for modulator therapy eligibility); nasal potential difference and intestinal current measurement for diagnostic equivocal cases. Care delivery in CFTR Foundation-accredited centers significantly improves outcomes.

CFTR modulator therapy has revolutionized CF treatment over past decade, transforming what was once a uniformly fatal pediatric disease into a chronic manageable condition with near-normal life expectancy in those treated early. Median predicted survival for CF patients born in 2020s is over 60 years (versus <10 years in 1970s, <40 years in 2010s). Modulators are oral small molecules that target the underlying CFTR protein defect in mutation-specific manner. Current approved modulators: ivacaftor (potentiator), lumacaftor/ivacaftor, tezacaftor/ivacaftor, elexacaftor/tezacaftor/ivacaftor (ETI). Approximately 90 percent of CF patients have at least one F508del allele making them eligible for ETI.