Wednesday, 5 September 2012

Cystic Fibrosis

Humans have 23 pairs of chromosomes on which genes are located. Genes code for particular proteins that are then synthesized and used in the body to carry out its basic functions (Reece, et al., 2008). However when there is a defect – or mutation - in one of these genes, the protein that is synthesized will also be affected (Reece, et al., 2008).

The most common genetically inherited disease in Caucasians is Cystic Fibrosis (CF), which mainly affects the respiratory system, pancreas and sweat glands (O'Sullivan & Freedman, 2009).  It occurs in approximately one in every 2500 live births. CF is caused by mutation in the Cystic Fibrosis transmembrane conductance regulator (CFTR) gene, which leads to changes in the consistency of the mucous found in airways (O'Sullivan & Freedman, 2009).

The CFTR gene is located on the long arm of chromosome 7 and is responsible for the coordination of chloride ions in and out of the cells (O'Sullivan & Freedman, 2009). When this gene is defected, the movement of chloride ions is restricted resulting in increased movement of sodium ions across the cell membrane from the intraluminal airway. The mucous lining becomes dehydrated and thick inhibiting the body’s cough clearance and mucocilliary clearance mechanisms and creating a medium for CF pathogen adherence (O'Sullivan & Freedman, 2009).

CF is an autosomal recessive disease; this means that both parents must carry the recessive gene for the child to have a one in four chance of receiving both recessive alleles and therefore having the disease (O'Sullivan & Freedman, 2009). If both parents are carriers then their offspring will have a 25% chance of  having the disease, 50% chance of becoming carriers and 25% chance of not receiving the gene at all (Torpy, 2009).



CF can effect various parts of the body because the CFTR protein is found in many parts of the body, however the disease maybe more prominent in some organs than others (Torpy, 2009). Early diagnosis of CF in infants is important as this allows for appropriate treatment to begin as soon as possible, however its diagnosis can be delayed if symptoms are attributed to asthma. It is important to consider Cystic Fibrosis when diagnosis of asthma is attributed with other unusual features such as severe respiratory infections, persistent coughing, viscous sputum production and abnormal chest shape or clubbing (O'Sullivan & Freedman, 2009).

The standard diagnostic procedure to identify CF is the sweat test, which involves measuring the sodium levels of sweat. In a person with CF the levels of Sodium will be higher due to their abnormal sweat gland function (O'Sullivan & Freedman, 2009). Genetic testing is also available to identify CFTR mutations and to identify carriers of the recessive CF gene (O'Sullivan & Freedman, 2009).

Currently there is no cure for CF however a range of treatments which have shown reasonable efficacy are available. These treatments include; chest physiotherapy techniques to help clear airways, intensive anti-biotic regime to combat respiratory infection and lung transplantation (O'Sullivan & Freedman, 2009).

Currently work work is also being done on Mutation-specific therapies which aim to fix class I and II mutations – premature termination die to stop codons resulting from single bases substitutions and faulty translation of proteins (O'Sullivan & Freedman, 2009). Also gene therapy where a copy of the uninfected gene is inserted into the infected cell seems promising in vitro, however in practice it still proves to be quite difficult and impractical (O'Sullivan & Freedman, 2009).

References


O'Sullivan, B. P., & Freedman, S. D. (2009, May 30). Cystic Fibrosis. www.thelancet.com , pp.1891-1904. Viewed 5 September 2012

Reece, J. B., Meyers, N., Urry, L. A., Cain, M. L., Wasserman , S. A., Minorsky, P. A., et al. (2008). Campbell Biology. Melbourne: Pearson.

Torpy, J. M. (2009). Cystic Fibrosis. JAMA: The Journal of the American Medical Association , 302 (10). Viewed 5 September 2012 <http://jama.jamanetwork.com.ezproxy.library.uq.edu.au/article.aspx?articleid=184548>

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