Cystic fibrosis

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What is it?

Cystic fibrosis (CF) is a relatively common inherited disease in which from infancy there are recurrent chest infections causing lung damage, intestinal malabsorption leading to severe malnutrition and growth failure, and there is an excess of salt in the sweat. Untreated the condition is usually fatal in infancy or early childhood.

The disease is caused by mutations in a pair of genes located on chromosome 7. Every cell in the body (except the sex cells) has 46 chromosomes (23 pairs, one of each pair inherited from the mother and the other from the father). Genes on these chromosomes form the body’s blueprint for producing proteins that control body functions. There is a gene on each number 7 chromosome that is responsible for the production of a protein called cystic fibrosis transmembrane regulator (CFTR). Mutations in this gene lead to absent or defective CFTR production, causing CF. More than 1,800 different CF mutations have been identified, although some are much more common than others, F508del (previously known as deltaF508) being the most common.

Since CF is recessive, an affected individual must have a mutation in each CFTR gene on each chromosome 7 in order to have the disease (one abnormal copy from each parent.) An individual with one working copy of the gene and one non-working copy will be a CF carrier. Carriers do not have symptoms of the disease, but they may pass the non-working copy of the gene on to their children. Therefore, both parents must be carriers or have CF themselves in order for their child to have CF. Caucasians from Northern Europe and Ashkenazi Jews have the highest population carrier rates (about 1 in 20-25).

Having CF means the absence of or defective production and function of CFTR. This leads to abnormal electrolyte and water movement in and out of the epithelial cells with thick, sticky mucus in the lungs and pancreas leading to respiratory infections and/or obstructed pancreatic and liver ducts leading to impaired fat and protein digestion. The majority of males with CF are also infertile due to missing or underdeveloped vas deferens, the tubules that transport sperm from the testes. Most people with CF will develop respiratory and pancreatic symptoms very early in life, although symptom severity will vary from person to person, even in those with the same mutations.

CF is one of the most common recessive genetic disorders in people of European origin. Currently, there is no prevention or cure, only treatment of the symptoms. However, research is being conducted to develop a cure and to enhance treatments. In fact, great strides in this effort have been made over the past 30 years, which are allowing people with CF to live longer lives of improved quality. The median survival is now over 30 years.

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