Most common Genetic disorder amongst the white population of Europe and North America.
Caused by a mutant recessive allele in which three dna bases , A,A,A are missing.
It is an example of a deletion mutation .
Deletion results in a single amino acid being left out of the protein.
The lack of this amino acid makes the protein unable to transport chloride ions across the epithelial membranes.
CFTR is a chloride ion channel protein that transports chloride ions out of the epithiel cells . Water then naturally follows by osmosis due to the water potential .
In cystic fibrosis the chloride ions do no leave so the epithelial membranes are therfore dry and the mucus they produce remains viscous and sticky.
Problems of cystic fibrosis
- Mucus congestion in the lungs provides an ideal breeding ground for bacteria this leads to a much higher risk of infecetion as the mucus traps disease causing microorganisms and cannot be removed.
- Breathing difficulties / less effective gas exchange
- Pancreatic duct can get blocked leading to not all of the food being digested. Causes the formation of fibrous cysts.
- Thick mucus in sperm ducts can cause males to be infertile
Gene replacement - defective gene is replaced with a healthy gene
Gene supplementation - In which one or more copies of the healthy gene are added alongside . The added genes have dominant alleles ,t he effects of the recessive alleles of the defective gene are masked.
Germ-line gene therapy involves replacing or suplementing the defective gene in the fertilised egg. This ensures that all the cells of the organism will develop normally, as will all the cells of their offspring . This is tehrefore a much more permanant solution .
Somatic cell gene therapy targets just teh affected tissues, such as the lungs, and the additional gene is therofre not present in the sperm or egg cell.