Genetic Diseases & Gene Therapy


What is a gene?

Genes are the little units of DNA that provide the blueprint for making a human being (or other animal, plant or microbe). With only a very few exceptions, every cell in the human body contains a complete set of genes housed on structures called chromosomes). Your chromosomes consist of the set of genes you get from your Mother, combined with a complementary set from your Father...thus, for the most part, you have 2 copies of each gene. Genes can be turned "on" or "off" depending on when and where they are needed. For example, there are certain genes that are only "on" while an embryo is developing into a fetus. Another example is certain cardiac genes that are turned "on" in the heart and are switched "off" everywhere else. Some genes determine interesting traits like eye color while others put you at risk for certain diseases.


What is a genetic disease?

Genes come in different "flavors." The genes for eye color come in many different "flavors" of brown, blue, green, etc. These different flavors have arisen naturally over the course of human evolution. But sometimes new flavors/different types of variation happen that aren't as harmless as a change of eye color. Some of these genes are the direct cause of illness (like Hemophilia or Huntington's Disease), some of these genes cause disease only when combined with certain environmental factors (like a gene(s) predisposing one to diabetes combined with poor nutrition and lack of exercise). Some disease genes have stuck around for a long time because, even though they make a person sick, they can also protect against other, more serious diseases. For example, people who get a copy of the sickle cell anemia gene from BOTH parents can get very ill, but if you carry one copy (only ONE parent has given you this "mutant" gene, the other gave you a "normal" gene), you are more resistant to malaria.


What is gene therapy?

Gene Therapy consists of trying to "fix" a disease-causing gene. This is quite complicated, as the way each disease gene causes disease can be quite different. Some genes cause disease because they are "broken" - so fixing them would require putting a nice new copy of the gene back in the cell. Some genes cause disease because they are too "aggressive" - so fixing them would require removing or otherwise interfering with the "aggressive" gene. Some diseases are caused by multiple genes and are much more difficult to try to correct. Unfortunately, most genetic diseases are in this latter category.

In theory, gene therapy could be done on an ill person's cells (called somatic gene therapy) in order to cure the person or it could be done on germ line (eggs/sperm) cells thus preventing the disease from being passed to an embryo (i.e. future generations). So far, gene therapy has been highly experimental, limited...and not very successful. In order to get new genes into human cells, viruses are used...and this is riddled with technical and safety problems. The immune system rejection and ensuring that the DNA that you are introducing will function inside the patient in question are also big hurdles. There is also a strong ethical component to the idea of gene therapy, especially on germ line cells. Instead of just preventing debilitating or fatal diseases from being passed on to progeny, will we run the risk, as a society, of trying to manipulate traits in our offspring that we consider less desirable? Eliminate birthmarks? Choose a certain eye color? Choose a certain gender? While right now this is still a bit of science fiction, it is really important to think about and discuss these possibilities and their implications in order to develop the wisdom to deal with them, if and when they happen. We also need to educate our kids about these issues, as the wise use of this technology will probably be up to future generations....

Gene therapy for Huntington's disease - New Scientist, 2003
Gene therapy for Parkinson's Disease - LA Times, October 2006


What is the Human Genome Project?

It was an international effort to determine the DNA sequence (every gene) that makes up a human being.
Interview with the Natl. Human Genome Research Instit. Deputy Director - He talks about the project's significance, implications for treatment of genetic diseases, ethics, and so forth.


What is genetic testing?

Thanks to the Human Genome Project, we have a "map" all the genes that make up a human body. And thanks to many different scientific research groups, we know how several of these genes cause disease. Genetic testing consists of taking a few cells from a person and "looking" at their DNA to see if they possess certain disease genes. Sounds simple? Not so fast....


The question is (are):

Useful Links

Information on specific genetic diseases:
What is a genetic disorder? - primer from the Univ. of Utah
Genetic Disorder Zone - information on various disorders (symptoms, treatment, personal stories)
Genes & Disease - an excellent on-line book covering over 80 human genetic disorders and the specific genes associated with them.
Genetic & Rare Disorders advocacy and support groups
Genetics Resources on the Internet from Pitt University
Natl Institutes of Health Genetic Disorders resource
CDC Office of Genomics and Disease prevention


Useful sites relating to gene therapy & testing:
A Report from the Howard Hughes Medical Institute on how genes that cause disease are discovered, why these mistakes occur, and what is being done to cure the diseases.
Gene Therapy, an overview
What is Gene Therapy? from the Human Genome Project
Article on Human Gene Therapy - from Georgetown Univ. (historical account, arguments for and against, etc.)
Understanding Gene Testing US Dept. Health & Human Services


Useful sites relating to the Human Genome Project (HGP):
National Human Genome Research Institute in particular, policy and ethics
UK Human Genome Mapping Project resource center
Ethical, legal and social implications of the HGP
US Dept. of Energy Genome Programs

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