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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