Cystic Fibrosis

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Cystic Fibrosis, or CF, is one of the most common inherited diseases in the Caucasian population with 1 in 2500 live births resulting in an infant born with CF, and with 1 in 25 people being heterozygous (carriers) for the condition. Cystic Fibrosis is a result of a mutation in the CFTR gene (Cystic Fibrosis Transmembrane Conductance Regulator), whereby the protein is incorrectly folded once it has been synthesised in the endoplasmic reticulum. The most commonly found mutation which causes approximately 85% of CF cases is the deletion of three nucleotides resulting in the removal of the amino acid, phenylamine. This mutation is known as ∆F508[1]. As a result of the mutation, most CFTR genes are broken down before they can be released from the plasma membrane.

The function of the CFTR gene is to act as a cAMP chlorine channel on the apical plasma membrane of most epithelial cells. For example, lining the respiratory tract and in the pancreas, thereby regulating the amount and composition of epithelial secretions. Unfortunately, without the CFTR gene, there is a disruption to the transport processes on the apical membrane. For example, a decrease in HCO3- and water secretion. The lack of water secretion causes a build-up of thick mucus either along the respiratory tract or the gastrointestinal (GI) tract. This build-up of mucus results in obstructions and tissue damage. In the GI tract, pancreatic juices cannot be released leading to food not being able to be digested correctly, hence malnutrition issues are common in patients with CF. The build-up of mucus in the respiratory tract causes recurrent infections, which are difficult to treat. A common infection which is caused by CF is bronchiectasis. This can form due to the build-up of mucus causing the airways to become blocked so they expand and stretch for gas exchange to occur[2]. Lung function decreases by approximately 2% each year, eventually resulting in a need for the patient to receive a lifesaving lung transplant[3].

As well as the mutation in the CFTR gene affecting the respiratory system, it also affects the digestive system. Mucus can build up in the intestines preventing digestive enzymes from sufficiently moving between the vital organs and therefore proteins, fats and vitamins cannot be broken down and absorbed by the body. This decreases the amount of nutrients found in the body which can lead to malnutrition[4].

Refereneces

  1. NCHPEG. Genetics and Nutrition: A resource for Dietetic Faculty and Practitioners: Cystic Fibrosis - Gene Mutations and CFTR Protein. 2016 [cited: 14/11/16]; Available from: URL:http://www.nchpeg.org/nutrition/index.php?option=com_content&view=article&id=462&itemid=564&limitstart=4
  2. NHS. Symptoms of Cystic Fibrosis. 2013 [cited: 15/11/16]; Available from: http://www.nhs.uk/Conditions/cystic-fibrosis/Pages/Symptoms.aspx
  3. Boron, W and Boulpaep, E (2009). Medical Physiology. 2nd ed. Philadelphia: Saunders Elsevier. p920.
  4. Mayo Clinic. Cystic Fibrosis: Symptoms and causes. October 2016 [cited: 15/11/16]; Available from: http://www.mayoclinic.org/diseases-conditions/cystic-fibrosis/symptoms-causes/dxc-20211893
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