Cystic fibrosis

- autosomal recessive

- carrier frequency in Caucasian (1:22)
- affects 1: 2500

- commonest abnormality is specific deletion at position 508 in amino acid sequence (chromosome 7, long arm)

- defect in CFTR (cystic fibrosis transmembrane conductance regulator)

- sweat test > 60mmol/L = diagnostic of CF (using pilocarpine iontophoresis)
- prolonged prothrombin time suggest both malabsorption of vitamin K and cirrhosis
- Burkholderia cepacia is seen in severe lung disease and associated with rapid deterioration.

- presenting signs (CF PANCREAS)

• Chronic cough and wheezing
• Failure to thrive
• Pancreatic insufficiency (symptoms of malabsorption like steatorrhea)
• Alkalosis and hypotonic dehydration
• Neonatal intestinal obstruction (meconium ileus)/ Nasal polyps
• Clubbing of fingers/ Chest radiograph with characteristic changes
• Rectal prolapse
• Electrolyte elevation in sweat, salty skin
• Absence or congenital atresia of vas deferens - males are almost always infertile
• Sputum with Staph or Pseudomonas (mucoid)

- human recombinant DNAase (dornase alfa 2.5mg daily) given as aerosol improve pulmonary function, decrease frequency of chest exacerbations

- Nebulised tobramycin may be given when airway pathogens are resistant to oral antibiotics


- Cystic fibrosis heterozygotes has an increased resistance to cholera


Causes of false positive sweat sodium test
- hypothyroidism
- familial hypoparathyroidism
- mucopolysaccharidoses
- alpha 1 antitrypsin deficiency
- Addison's disease