Gene+Therapy

**What is gene therapy? ** Genes, which are carried on chromosomes, are the basic physical and functional units of heredity. Genes are specific sequences of bases that encode instructions on how to make proteins. Although genes get a lot of attention, it’s the proteins that perform most life functions and even make up the majority of cellular structures. When genes are altered so that the encoded proteins are unable to carry out their normal functions, genetic disorders can result. Gene therapy is a technique for correcting defective genes responsible for disease development. Researchers may use one of several approaches for correcting faulty genes:
 * A normal gene may be inserted into a nonspecific location within the genome to replace a nonfunctional gene. This approach is most common.
 * An abnormal gene could be swapped for a normal gene through homologous recombination.
 * The abnormal gene could be repaired through selective reverse mutation, which returns the gene to its normal function.
 * The regulation (the degree to which a gene is turned on or off) of a particular gene could be altered.

**How does gene therapy work? ** In most gene therapy studies, a "normal" gene is inserted into the genome to replace an "abnormal," disease-causing gene. A carrier molecule called a vector must be used to deliver the therapeutic gene to the patient's target cells. Currently, the most common vector is a virus that has been genetically altered to carry normal human DNA. Viruses have evolved a way of encapsulating and delivering their genes to human cells in a pathogenic manner. Scientists have tried to take advantage of this capability and manipulate the virus genome to remove disease-causing genes and insert therapeutic genes. Target cells such as the patient's liver or lung cells are infected with the viral vector. The vector then unloads its genetic material containing the therapeutic human gene into the target cell. The generation of a functional protein product from the therapeutic gene restores the target cell to a normal state. Some of the different types of viruses used as gene therapy vectors: Besides virus-mediated gene-delivery systems, there are several nonviral options for gene delivery. The simplest method is the direct introduction of therapeutic DNA into target cells. This approach is limited in its application because it can be used only with certain tissues and requires large amounts of DNA. Another nonviral approach involves the creation of an artificial lipid sphere with an aqueous core. This liposome, which carries the therapeutic DNA, is capable of passing the DNA through the target cell's membrane. Therapeutic DNA also can get inside target cells by chemically linking the DNA to a molecule that will bind to special cell receptors. Once bound to these receptors, the therapeutic DNA constructs are engulfed by the cell membrane and passed into the interior of the target cell. This delivery system tends to be less effective than other options. Researchers also are experimenting with introducing a 47th (artificial human) chromosome into target cells. This chromosome would exist autonomously alongside the standard 46 --not affecting their workings or causing any mutations. It would be a large vector capable of carrying substantial amounts of genetic code, and scientists anticipate that, because of its construction and autonomy, the body's immune systems would not attack it. A problem with this potential method is the difficulty in delivering such a large molecule to the nucleus of a target cell.
 * **Retroviruses **<span style="font-family: 'Arial','sans-serif'; font-size: 12pt;"> - A class of viruses that can create double-stranded DNA copies of their RNA genomes. These copies of its genome can be integrated into the chromosomes of host cells. Human immunodeficiency virus (HIV) is a retrovirus.
 * **<span style="font-family: 'Arial','sans-serif'; font-size: 12pt;">Adenoviruses **<span style="font-family: 'Arial','sans-serif'; font-size: 12pt;"> - A class of viruses with double-stranded DNA genomes that cause respiratory, intestinal, and eye infections in humans. The virus that causes the common cold is an adenovirus.
 * **<span style="font-family: 'Arial','sans-serif'; font-size: 12pt;">Adeno-associated viruses **<span style="font-family: 'Arial','sans-serif'; font-size: 12pt;"> - A class of small, single-stranded DNA viruses that can insert their genetic material at a specific site on chromosome 19.
 * **<span style="font-family: 'Arial','sans-serif'; font-size: 12pt;">Herpes simplex viruses **<span style="font-family: 'Arial','sans-serif'; font-size: 12pt;"> - A class of double-stranded DNA viruses that infect a particular cell type, neurons. Herpes simplex virus type 1 is a common human pathogen that causes cold sores.

**<span style="font-family: 'Arial','sans-serif'; font-size: 16pt;">What are some of the ethical considerations for using ** **<span style="font-family: 'Arial','sans-serif'; font-size: 16pt;">gene therapy? **

**<span style="font-family: 'Arial','sans-serif'; font-size: 12pt;">Some Questions to Consider ** · <span style="font-family: 'Arial','sans-serif'; font-size: 12pt;">Are disabilities diseases? Do they need to be cured or prevented? · <span style="font-family: 'Arial','sans-serif'; font-size: 12pt;">Does searching for a cure demean the lives of individuals presently affected by disabilities? · <span style="font-family: 'Arial','sans-serif'; font-size: 12pt;">Is somatic gene therapy (which is done in the adult cells of persons known to have the disease) more or less ethical than germline gene therapy (which is done in egg and sperm cells and prevents the trait from being passed on to further generations)? In cases of somatic gene therapy, the procedure may have to be repeated in future generations. · <span style="font-family: 'Arial','sans-serif'; font-size: 12pt;">Preliminary attempts at gene therapy are exorbitantly expensive. Who will have access to these therapies? Who will pay for their use?

<span style="font-family: 'Arial','sans-serif'; font-size: 12pt; line-height: 115%; margin: 0cm 0cm 10pt;">People have had to deal with genetic inequality as a fact of life. With the advent of gene therapy, this may no longer be the case for some people. Most people feel that it is okay to use gene therapy to treat human genetic diseases. Somewhat surprisingly. Some individuals, however, are concerned that the technique may be used for "treatment" of genetic "disorders" other than diseases. <span style="font-family: 'Arial','sans-serif'; font-size: 12pt; line-height: 115%; margin: 0cm 0cm 10pt;">Because many people are concerned about the safety of gene therapy, a special committee of the National Academy of Science was created to look into the consequences of releasing rDNA engineered organisms into the environment. The committee concluded that "there is no evidence that unique hazards exist either in the use of rDNA technique or in the transfer of genes between unrelated organisms," and that, "the risks associated with the introduction of rDNA engineered organisms are the same kind as those associated with the introduction of unmodified organisms."

**<span style="font-family: 'Arial','sans-serif'; font-size: 20pt; line-height: 115%;"> STEPS **

**<span style="font-family: 'Arial','sans-serif'; font-size: 12pt; line-height: 115%;">Five Basic Steps **<span style="font-family: 'Arial','sans-serif';"> The use of gene therapy has five basic steps, and there are a variety of methods to achieve each step. <span style="font-family: 'Arial','sans-serif'; font-size: 12pt; line-height: 115%;">
 * <span style="font-family: 'Arial','sans-serif';">· Step 1 **<span style="font-family: 'Arial','sans-serif';">: The gene coding for the desired protein is isolated.

<span style="font-family: 'Arial','sans-serif';">· ** Step 2 **: The gene is delivered to a target cell by means of a vector. This vector carries the gene and gets it into the cell. for the protein.
 * <span style="font-family: 'Arial','sans-serif';">· Step 3 **<span style="font-family: 'Arial','sans-serif';">: The cell integrates this gene and begins to produce DNA and RNA coding
 * <span style="font-family: 'Arial','sans-serif';">· Step 4: **<span style="font-family: 'Arial','sans-serif';"> The protein is made by the cell.

then stimulates the desired action such as spinal fusion or disc regeneration.
 * <span style="font-family: 'Arial','sans-serif';">· Step 5: **<span style="font-family: 'Arial','sans-serif';"> This protein acts inside the cell or is released into the environment and