Genetic disease which leads to abnormally viscous mucus which blocks many structures including the conducting airways and lungs → results in repeated chest infections and chronic colonisation
Aetiology
Autosomal recessive mutation caused by a mutation in chromosome 7 at the CF transmembrane conductance regulator (CFTR) gene
Carrier rate 1/25 in UK
Most common in Caucasians
Pathophysiology
CFTR protein normally forms a channel on mucosal surfaces that allows chloride ions out of the cell and into the lumen (e.g. lumen of airway)
In the lungs and GI tract, failure of CFTR results in reduced Cl- secretion into the lumen
Na+ normally follows Cl-so Na+ secretion is also reduced
Less Na+ in lumen = increased water reabsorption from lumen into epithelial cells
Results in a viscous mucus which blocks ducts and impairs mucosal defence
In the sweat glands, failure of CFTR results in excess Cl- (and Na+) in the sweat
Mutations have been divided into different classes, depending on their effect on CFTR
Pseudomonas infections is associated with worse prognosis
By adulthood most patients will have a chronic Pseudomonas infection with a unique strain of Pseudomonas - adults with CF advised not to mix
Clinical features
Classical presentation - child aged 0-2 with recurrent infections, large offensive stools and failure to thrive