CF treatments for the future

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CF treatments for the future

Effective gene therapy would treat the cause rather than the symptoms of the disease. In gene therapy the genotype and hence the phenotype of target cells (those affected by the disease) is altered. This is achieved as follows:

  • Normal alleles of the gene are inserted into target cells, either using genetically modified virus to infect the target cells or using liposomes.
  • The normal form of the gene is transcribed and translated
  • A functioning protein is produced in the target cells 

In the case of the CF gene, a functioning CFTR protein is produced and incorporated into the cell membrane, thus restoring the ion channel and avoiding the symptoms of CF.

How genes are inserted using viruses
In the virus, the DNA sequence that allows it to replicate is removed. This is replaced with the normal allele of the desired gene, along with promoter sequence that initiates transcription and translation of the gene. The use of viruses is a potentially efficient form of gene transfer but it has been found to produce an inflammatory response, with treated patients experiencing symptoms such as headache, fatigue, fever and raised heart rate. 

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CF treatments for the future

How genes are inserted using liposomes
First, a copy of the normal allele is inserted into a loop of DNA (called a plasmid). The plasmids are then combined with liposomes (spherical phospholipid bilayers). The positively charged head groups of the phospholipds combine with the DNA to form a liposome-DNA complex.
The CF patient breathers in aerosol containing these complexes using a nebuliser. The liposomes fuse with epithelial cell membranes and carry the DNA into the cells.

Genetic testing
Genetic testing can be performed on any DNA, so it is possible to take samples of cheek cells, white blood cells or cells obtained from a foetus or embryo. The DNA is tested to see whether it contains the known base sequences for the most common mutations that cause CF.
Genetic testing can confirm a diagnosis of CF. However since there are a large number of different mutations of the CFTR gene which cause the disease, a negative result must be treated with caution.
Genetic testing can identify carriers. A sample of blood or cells taken from inside the mouth can be used to detect abnormal alleles in people without the disease who are heterozygous

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