Cystic Fibrosis

CLINICAL CHARACTERISTICS

Cystic fibrosis (CF) is a multisystem disease affecting epithelia of the respiratory tract, exocrine pancreas, intestine, hepatobiliary system, and exocrine sweat glands. Morbidities include recurrent sinusitis and bronchitis, progressive obstructive pulmonary disease with bronchiectasis, exocrine pancreatic deficiency and malnutrition, pancreatitis, gastrointestinal manifestations (meconium ileus, rectal prolapse, distal intestinal obstructive syndrome), liver disease, diabetes, male infertility due to hypoplasia or aplasia of the vas deferens, and reduced fertility or infertility in some women. Pulmonary disease is the major cause of morbidity and mortality in CF.

DIAGNOSIS/TESTING: The diagnosis of CF is established in a proband with (1) elevated immunoreactive trypsinogen on newborn screen, signs and/or symptoms suggestive of CF, or family history of CF; AND (2) evidence of an abnormality in cystic fibrosis transmembrane conductance regulator (CFTR) function: sweat chloride ≥60 mmol/L on sweat chloride testing, biallelic CF-causing pathogenic variants, or nasal transmembrane epithelial potential difference measurement consistent with CF.

MANAGEMENT

CFTR modulator therapy is available for individuals with responsive variants. Newborns: management by a CF specialist or CF care center; airway clearance instruction; encouraging feeding with breast milk; routine vaccinations; contact precautions with every encounter; antibiotics for bacterial suppression and treatment; nutrition management; pancreatic enzyme replacement; nutrient-dense food and supplements; fat-soluble vitamin supplements; laxative treatment as needed with surgical management for bowel obstruction; and salt and water supplementation. After the newborn period: airway clearance; pulmonary treatment (bronchodilator, hypertonic saline, dornase alfa, airway clearance, inhaled corticosteroids and/or long-acting beta agonist, and aerosolized antibiotic); standard treatments for pneumothorax or hemoptysis; double lung transplant for those with advanced lung disease; routine vaccinations including influenza; contact precautions; antibiotics for bacterial suppression and treatment; antibiotics and/or surgical intervention for nasal/sinus symptoms; nutrition management; pancreatic enzyme replacement; nutrient-dense food and supplements; fat-soluble vitamin supplements; laxative treatment as needed with surgical management for bowel obstruction; standard treatments for gastroesophageal reflux disease; oral ursodiol for biliary sludging/obstruction; liver transplant when indicated; management of CF-related diabetes mellitus by an endocrinologist; assisted reproductive technologies (ART) for infertility; salt and water supplementation; standard treatments for associated mental health issues. Frequent assessment by a CF specialist to monitor for new or worsening manifestations; pulmonary function testing frequently after age five years; chest radiograph or chest CT examination to assess for bronchiectasis every two years or as needed; cultures of respiratory tract secretions at least every three months; non-tuberculosis mycobacterium culture and serum IgE annually or as indicated; annual CBC with differential; annual ENT assessment; monitoring growth and GI manifestations at each visit; fecal elastase as needed; annual serum vitamin A, D, E, and PT (as a marker of vitamin K); annual liver function tests; annual random glucose, annual two-hour glucose tolerance test beginning at age ten years; DXA scan as needed in adolescence; infertility assessment as needed; annual electrolytes, BUN, and creatinine; annual assessment of depression and anxiety. Environmental smoke, exposure to respiratory infections, dehydration. Molecular genetic testing of at-risk sibs (if the pathogenic variants in the family are known) or sweat chloride testing of at-risk sibs (if the pathogenic variants in the family are not known) to identify as early as possible those who should be referred to a CF center for initiation of early treatment.

GENETIC COUNSELING

CF is inherited in an autosomal recessive manner. If both parents are known to be heterozygous for a pathogenic variant, each sib of an affected individual has at conception a 25% chance of being affected, a 50% chance of being heterozygous, and a 25% chance of inheriting neither of the familial pathogenic variants. Once the pathogenic variants have been identified in an affected family member, targeted heterozygote testing for at-risk relatives and prenatal/preimplantation genetic testing for CF are possible.