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Key Points

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  • Disease summary:

    • Cystic fibrosis (CF) is the most common genetically inherited autosomal recessive disease in Caucasians that leads to multisystem organ dysfunction with the majority of morbidity and mortality related to respiratory and gastrointestinal (GI) systems.

    • CF arises secondary to mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene on the long arm of chromosome 7; CFTR is translated into a multidomain chloride ion channel belonging to ATP-binding cassette (ABC) transporter superfamily.

    • Greater than 1800 CFTR mutations are known and may be classified by their functional defect; each mutation leads to varying impact on salt and water balance.

    • The pathogenesis of CF involving the lungs includes a vicious cycle of infection, inflammation, and bronchiectasis.

    • The clinical course of CF is typically chronic or progressive punctuated by acute exacerbations and eventual respiratory failure. As patient survival improves, other organ system complications are increasingly identified and require therapy.

  • Hereditary basis:

    • Autosomal recessive pattern with variable clinical phenotype affected by the specific CFTR mutation, modifier genes, and environment

  • Differential diagnosis:

    • Bronchiectasis from other causes: primary ciliary dyskinesia, tuberculosis, chronic aspiration

    • Primary immune deficiency, for example common variable immune deficiency

    • Other causes of elevated sweat chloride levels: malnutrition, hypothyroidism, adrenal insufficiency

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Diagnostic Criteria and Clinical Characteristics

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Diagnostic Criteria

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  • Clinical presentation (one or more typical clinical findings)

  • Sweat chloride concentration greater than or equal to 60 mol/L (40-59 mmol/L considered indeterminate, <40 mmol/L considered negative)

  • CFTR mutation analysis indicating two known CF disease-causing mutations in trans configuration (Table 114-1). Mutation analysis may include the attempted identification of polymorphisms, deletions, and duplications

  • Newborn screening: Evidence of elevated immune-reactive trypsinogen (IRT) and/or identification of one or more disease-causing CFTR mutation triggers sweat chloride testing and more extensive CFTR mutation analysis

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  • Other considerations:

    • CF-related metabolic syndrome (CRMS) is a new term proposed for patients who are asymptomatic but have either nondiagnostic sweat chloride or CFTR mutation analysis concerning for, but not diagnostic of cystic fibrosis.

    • CFTR-related disorder (CRD) is a term proposed for CRMS patients who are symptomatic in some way.

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Table Graphic Jump Location
Table 114-1CFTR Mutation Classification
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Clinical Characteristics

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Progressive pulmonary disease due to chronic infection, airway inflammation, and bronchiectasis is associated with the greatest morbidity and mortality in patients with CF. However, CF is a multisystem disorder (Table 114-2), a result of CFTR expression in most organs of the body, with varying clinical presentation that requires a multidisciplinary approach to treatment.

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Table Graphic Jump Location
Table 114-2CF Organ System Involvement

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