The Cystic Fibrosis Gene
Uploaded by Admin on Jan 22, 1999
Introduction
Cystic fibrosis is an inherited autosomal recessive disease that exerts its main effects on the digestive system and the lungs. This disease is the most common genetic disorder amongst Caucasians. Cystic fibrosis affects about one in 2,500 people, with one in twenty five being a heterozygote. With the use of antibiotics, the life span of a person afflicted with CF can be extended up to thirty years however, most die before the age of thirteen.1 Since so many people are affected by this disease, it's no wonder that CF was the first human genetic disease to be cloned by geneticists. In this paper, I will be focusing on how the cystic fibrosis gene was discovered while at the same time, discussing the protein defect in the CF gene, the bio-chemical defect associated with CF, and possible treatments of the disease.
Finding the Cystic Fibrosis Gene
The classical genetic approach to finding the gene that is responsible for causing a genetic disease has been to first characterize the bio-chemical defect within the gene, then to identify the mutated protein in the gene of interest, and finally to locate the actual gene. However, this classical approach proved to be impractical when searching for the CF gene. To find the gene responsible for CF, the principle of "reverse genetics" was applied. Scientists accomplished this by linking the disease to a specific chromosome. After this linkage, they isolated the gene of interest on the chromosome and then tested its product.2Before the disease could be linked to a specific chromosome, a marker needed to be found that would always travel with the disease. This marker is known as a Restriction Fragment Length Polymorphism or RFLP for short. RFLP's are varying base sequences of DNA in different individuals which are known to travel with genetic disorders.3 The RFLP for cystic fibrosis was discovered through the techniques of Somatic Cell Hybridization and through Southern Blot Electrophoresis (gel separation of DNA). By using these techniques, three RFLP's were discovered for CF; Doc RI, J3.11, and Met. Utilizing in situ hybridization, scientists discovered the CF gene to be located on the long arm of chromosome number seven. Soon after identifying these markers, another marker was discovered that segregated more frequently with CF than the other markers. This meant the new marker was closer to the CF gene. At this time, two scientists named Lap-Chu Tsui and Francis Collins were able...