University of Bristol
Wellcome Trust
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PEEP for Physics & Ethics at GCSE

Genes and health

Cystic fibrosis

Cystic fibrosis is caused by a faulty gene on chromosome 7, which was discovered in 1989. To date there are over 1,300 known ways in which this gene may be faulty, but these fall into 5 or 6 main groups. This gene carries the code for the manufacture of a protein known as CFTR (Cystic Fibrosis Transmembrane Conductance Regulator), which transports salt and water in and out of the cells that line the lungs and digestive system. Because we have a pair of each chromosome, and therefore of each gene, you only need one working copy of this gene to produce enough of this protein. But if both copies, one inherited from each parent, are faulty then the body cannot produce the fully functioning version of the CFTR protein. Usually, in CF the protein gives out too much salt and too little water, which is why sticky mucus clogs the lungs and there is extra salt in the sweat.

The research into treatment of CF falls into two main categories; gene therapy and drug based treatments of the symptoms of the disease. Even drug development is informed by the knowledge of how the gene defects interrupt the production of fully functioning CFTR. For example some antibiotics, gentomicin for example, act by overcoming the presence of a premature stop gene which makes the protein manufacture stop before the sequence is complete.

The symptoms of CF are obvious from birth. However, treatments are improving all the time as are the quality of life and life expectancy of sufferers. CF once meant children rarely reached adulthood, now patients are living longer.

It is estimated that one in 25 people in the UK carry a mutation of the CF gene. People with one mutation-free CF gene are free of symptoms, you have to have two genes with mutations before there is a problem. So for a child to have CF, both parents must be carriers. Even when both parents are carriers they will not necessarily have a child with the disease, or even who is a carrier.

 Huntingdon’s disease


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 Cystic Fibrosis Trust  
 Articles on research into CF

Activity  Question:
What are the chances of parents who are both carriers having a child with CF?