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About CF » Pathophysiology of CF

Pathophysiology of CF

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Mutations in the CFTR gene can affect the quantity and/or the function of CFTR channels at the cell surface. The type of mutation has a significant impact on the extent of abnormal chloride transport and, consequently, on the patient’s symptoms.

Airway

Pulmonary disease is the most challenging aspect of managing CF and is the main cause of mortality. CFTR dysfunction is associated with a change in the composition and quantity of the airway surface liquid resulting in impaired clearance of bacteria from the airway.

Sweat gland

Elevated sweat chloride is a hallmark symptom of CF and is used as a diagnostic marker. Abnormal CFTR inhibits the reabsorption of chloride from sweat into the cells lining the sweat duct. Retention of chloride ‘traps’ sodium ions on the skin surface leading to characteristic salty sweat.5

Liver

Although liver abnormalities are not considered a dominant manifestation in CF, 25% of sufferers of CF show signs of liver disease and about 6–8% have established cirrhosis.3 CFTR dysfunction can lead to increased viscosity of bile, obstructing hepatic ducts and causing focal biliary cirrhosis.

Pancreas

About 85–90% of people with CF suffer from pancreatic insufficiency, with symptoms including diarrhoea, abdominal pain, excessive bowel gas, malabsorption of nutrients and failure to thrive.1 These symptoms are caused by thickened exocrine secretions obstructing pancreatic ducts, leading to accumulation of digestive enzymes in the pancreas and auto-digestion of pancreatic tissue.2

GastrointestinaI tract

Gastrointestinal (GI) abnormalities are frequently seen in CF and result in malabsorption of essential nutrients from the gut. Reduced chloride and water secretion into the gut can cause two predominant conditions: meconium ileus at birth and distal intestinal obstruction syndrome (DIOS) later in life.4

Reproductive system

Virtually all men with severe CF are infertile due to a condition called congenital bilateral absence of the vas deferens (CBAVD). As the male reproductive system develops in the uterus, abnormal CFTR leads to obstruction of the vas deferens with mucus, resulting in atrophy.

References
  1. Davis PB et al. Am J Respir Crit Care Med 1996;154:1229–56
  2. Sturgess JM. J Pedia r Gastroenterol Nutr 1984;3(Suppl 1):S55–66
  3. Bush A et al (Eds). Cystic Fibrosis in the 21st Century. Progress in Respiratory Research. Basel, Karger. 2006;34:251–61
  4. Littlewood JM et al. J R Soc Med 1992;85(Suppl 19):13–19
  5. Davis PB. Am J Respir Crit Care Med 2006;173:475-82