Gene Therapy For Heart disease

Situated in a row along the length of each chromosome are the genes which carry the instructions for a particular characteristic.  A gene is a long segment of the molecule deoxyribonucleic acid, or DNA. The segment, composed of minute subunits called nucleotide bases, serves as the blueprint for manufacturing a single protein or enzyme needed for the structure or function of cells. In humans, genes are compressed and bundled into a set of 23 pairs of chromosomes, which stabilize and protect the DNA. Even a tiny error in the arrangement of a gene’s nucleotide bases can lead to the production of a protein or enzyme that works improperly or the needed compounds might not be produced at all.

Gene therapy, a technique for correcting defective genes, is offering new and exciting possibilities for curing and treating several genetic disorders. Instead of treating the symptoms of a disorder, gene therapy alters the genetic makeup of certain cells.  The original goal of gene therapy was to substitute a healthy gene for a defective one or to repair a faulty gene, thereby eliminating symptoms of disease. But researchers have moved beyond inherited genetic disorders to treat other kinds of diseases. Today, almost 75 percent of all clinical trials involving gene therapy are aimed at treatments for cancer and acquired immunodeficiency syndrome. Other new gene therapy projects are targeted at conditions such as heart disease. Eventually, gene therapy might help older people regain strength in withered muscles and increase pumping power in aging hearts.

Types of Gene Therapy

The two forms of gene therapy currently used involve somatic gene therapy, which involves introducing a “good” gene into targeted cells with the end result of treating the patient. This type of therapy does not treat the patient’s future children since these genes are not passed along to offspring. This is the more common form of gene therapy that is being performed throughout the world.

The second type of gene therapy is germ line gene therapy, which involves modifying the genes in egg or sperm cells. This therapy is aimed at either correcting defective genes responsible for certain diseases or enhancing the genetic makeup of one’s offspring. Contrary to somatic cell gene therapy, which affects only the target cells of the individual being treated, germ line therapy has permanent hereditary consequences. Although it has the potential for preventing inherited disease, germ line gene therapy for the purpose of enhancing future generations has stirred great controversy.

In patients with coronary artery blockages that cannot be treated with PTCA  or CABG , genes are transferred directly into a targeted tissue (in this case the heart muscle), where the gene “turns on” DNA that causes cells to produce the proteins that cause growth of new blood vessels. These new blood vessels will increase the amount of blood reaching the heart muscle and will help to get rid of the patient's angina or chest pain.

Researchers have developed several methods for transporting genes into cells. The most common technique is to attach healthy genes to genetically modified viruses. These infectious agents, known as vectors, carry the genes into a cell’s nucleus and incorporate them into the genetic material of the infected cell. The adenovirus is one such viral particle that efficiently transfers genes to tissues such as the myocardium, or heart muscle. Genes transferred by adenovirus remain in the tissue they are sent to and are active for only one or two weeks. This is important because it potentially prevents the overproduction of a protein that might cause abnormal blood vessel growth.

Another gene delivery method, one that still is under development, is chimeraplasty, in which segments of DNA are inserted into a cell’s nucleus. The DNA segment binds with a defective gene in a way that helps the cell’s repair mechanisms identify and fix the defective gene.

Gene therapy is a powerful new technology, but much research remains to be done before this approach to the treatment of disease realizes its full potential. Despite some technical setbacks, most experts believe the use of gene therapy in medicine is inevitable. Experts also believe within the next few decades doctors routinely will be able to correct simple genetic defects, eliminating a number of diseases that now destroy humankind.