Gene Therapy for Heart Disease
Dateline: 10/03/99
Genetic manipulation to treat heart disease is, without question, the most exciting development in the field of cardiology in recent times. Experimental studies have suggested the possibility of growing new blood vessels to treat coronary artery disease, of giving heart muscle the ability to pump more strongly and thereby reverse heart failure, and maybe to even replace the defective genes that result in some forms of congenital heart disease.
In this week's article, I will briefly introduce you to the fascinating field of medical genetics. In future articles, we'll take a look at each of the potential applications in treating heart disease.
What is a gene ?
Everything about the human body - its structure, skin texture, organ function, brain development, eye color, and much more - is controlled by special nucleic acids called genes. The first evidence of this was uncovered by Watson and Crick, when they unravelled the mystery of a material called DNA - short for De-oxyribo Nucleic Acid.
This DNA is contained in small packages called Genes. Many genes, together, make up a chromosome. Each cell in the human body has 46 such chromosomes. In short, then, a gene is the very basic building block, the smallest functional unit of the human genetic make-up.
How do genes affect structure and function ?
Genes are made up of nucleic acid primers called nucleotides, arranged in a specific sequence. This pattern of arrangement is responsible for their controlling function. Let me try and explain with an example.
There is a gene that controls the production of a enzyme (a substance that affects the rate of chemical reactions) called G6PD. This is an essential enzyme found in red blood cells. The enzyme prevents the formation of destructive free radicals. If this gene is defective, G6PD will not be formed. The free radicals will accumulate inside the red cells, and finally destroy them, resulting in anemia.
Different genes control different unique structural and functional units like this. The effect of defective genes can manifest as a malfunction in the relevant organ system.
What is gene therapy ?
Once scientists identified genes, and recognized their effects on human disease, the logical next step was to try and influence this process. In this way, diseases can be treated.
As a first step, researchers were able to generate artificial copies of normal genes in the laboratory. These were identical in every respect to the normal gene, and could faithfully reproduce their function inside the human body. But how to get the artificial gene in there ?
Gene delivery processes
For a long time, this question confounded scientists. Until the answer came in the form of studies on viruses. Viruses cause many human diseases like the flu and common cold. A virus is essentially a package of DNA inside an envelope. They attack humans by entering cells and then attaching their DNA to the human DNA inside that cell !
Could this process be exploited for beneficial purposes ? Excited about the possibility, researchers moved ahead fast. Soon they tasted success. Today, the adeno-virus is used as a delivery vehicle for gene transfer. Essentially, this procedure involves the following steps:
- inactivate the virus by destroying all the harmful DNA inside it
- insert the artificial gene into the virus
- allow the virus carrying the artificial gene to enter the human recepient and "attack" the target tissue
The procedure today is still at a very rudimentary stage of development. Fine tuning is still required in the delivery process. Selective insertion of the virus into only the desired organ would be ideal. Better still would be a way to insert the artificial gene in exactly the same location that the defective gene was. Another bug-bear is getting the inserted artificial gene to reproduce whenever cells divide and regenerate. Otherwise, the beneficial effect would only last as long as the cell was alive.
What does the future hold ?
Plenty of excitement, for sure. While some of the obstacles seem formidable, many brilliant scientists are working on solutions. Already gene therapy for angina and heart failure are undergoing clinical trials. The day is not far off when the treatment will be sufficiently advanced to be applicable for a general population.
For more resources on gene therapy, you can
- visit the archives for related articles
- visit the resource library
- check out the heart disease bookstore
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