D3: Detection and Diagnosis of DiseaseImaging you have flu symptoms and decide to hit up the doctor. The doctor suspects you may have the H1N1 flu virus strain. There is a rapid test that the doctor performs and concludes that you do have H1N1. RT-PCR analysis can also be performed on a sample to diagnosis the virus. Using the same procedure described earlier, primers have been designed for a specific H1N1 mRNA. Detection of H1N1 mRNA levels using RT-PCR is more sensitive than a rapid test. RT-PCR can also be used to detect HIV, SARS, Dengue Virus, and mumps, just to name a few.
If the gene sequence that contributes to a genetic condition is known, it should be able to be identified by PCR. Now that we know the sequence of the human genome, scientists have been able to link a particular disease to a gene or set of genes. Sickle cell anemia, cystic fibrosis and hemophilia are just a few conditions where the gene has been identified. PCR primers specific for these genes can be used to identify and amplify these genes. This can occur before symptoms of the diseases are even noticed.
Gene TherapyGenes may be changed such that they result in a protein that is unable to do its job. Knowing the original sequence of the gene, scientists have been devising methods to deliver the original sequence of the gene back into the cells. This is gene therapy.
While it sounds great and makes sense biologically, gene therapy has faced many obstacles. First of all, how do you get the gene into the cells? Usually, viral vectors are the vehicles of choice. In the example below, an adenovirus vector is used to deliver the correct or normal gene into the cell.
Image from here.
This method was used in trials in 2000 to treat ten children with severe combined immunodeficiency. David Vetter, otherwise known as the "Bubble Boy," had this condition. Nine children showed significant improvement, but three children later developed leukemia, which killed one child.
Some other issues with gene therapy still need to be hammered out. Currently, the effect is not long-lasting. The correct gene needs to be incorporated into the genome so that its protein is continually being produced.
Gene therapy introduces something foreign into human cells. This can send a red flag to the immune system. The immune system has a great memory making it difficult to administer several treatments without an immune response.
The viral vectors used may also be problematic in targeting only certain cells. Also, they may be toxic.Finally, many diseases result from problems in several genes. Gene therapy can only target single genes.
PharmaceuticalsThe DNA sequence of a gene can be used to determine the amino acid sequence of its corresponding protein. This information, as well as experiments performed in the lab, can be used to determine the 3D structure of the protein or molecule, and you won't even need your 3D glasses. Knowing how the structure of the protein relates to its function allows scientists to don their lab coats and head into the lab to engineer similar proteins or small molecules. These can then be screened for desired effects.
Selective Estrogen Receptor Modulators, or SERMs, are examples of molecules that have been produced to bind to estrogen receptor. Knowing the structure of estrogen and its receptor, scientists have been able to generate other molecules that can bind estrogen receptor. They then can select for molecules that function as estrogens or anti-estrogens.
Earlier we discussed gene cloning. This technique can be used to produce large amounts of protein. The gene coding for a protein of interest can be cloned into an expression vector and transferred to host organism such as bacteria, insects, and so on. The vector is expressed, and boatloads of protein can be made. The insulin diabetics use to regulate their blood sugar is produced in this way.
Whole animals have been created that express a gene that is often from another species. These are transgenic animals. They are also called genetically modified organisms, which we will talk more about it a bit.
In order to make a transgenic organism, an egg from a species is removed and fertilized in vitro. The gene of interest is cloned and injected into nuclei of fertilized eggs in hopes the transgene will be integrated into the genome. The transgenic fertilized eggs are then implanted in a surrogate. The end result is a transgenic animal.
Transgenic goats and chickens have been produced this way. The protein product of the transgene is found in the milk and the egg, respectively. The proteins can then be isolated and purified.