Gene Therapy

Gene Therapy: It’s Mechanism

Several approaches to gene therapy are being tested, including:

• Replacing a mutated gene that causes disease with a healthy copy of the gene

• Inactivating, a mutated gene that is functioning improperly

• Introducing a new gene into the body to help fight a disease

In general, a gene cannot be directly inserted into a person’s cell. It must be delivered to the cell using a carrier. Vector systems can be divided into Viral vectors and Non-viral vectors.

Viral vectors are a tool commonly used by molecular biologists to deliver genetic material into cells. This process can be performed inside a living organism (in vivo) or in cell culture (in vitro). Viruses have evolved specialized molecular mechanisms to

efficiently transport their genomes inside the cells they infect.

Key properties of a viral vectors:

Safety. Although viral vectors are occasionally created from pathogenic viruses, they are modified in such a way as to minimize the risk of handling them. This usually involves the deletion of a part of the viral genome critical for viral replication. Such a virus can infect cells but, once the infection has taken place, requires a helper virus to provide the missing proteins for production of new virions.

Low toxicity. The viral vector should have a minimal effect on the physiology of the cell it infects.

Stability. Some viruses are genetically unstable and can rapidly rearrange their genomes. This is detrimental to predictability and reproducibility of the work conducted using a viral vector and is avoided in their design.

Cell type specificity. Most viral vectors are engineered to infect as wide a range of cell types as possible. However, sometimes the opposite is preferred. The viral receptor can be modified to target the virus to a specific kind of cell.

Non-viral vectors typically consist of DNA or RNA which may be delivered to the target cell usually with the aid of a delivery vehicle. Delivery vehicles may be based around lipids (such as liposomes) which fuse with the cell membrane releasing the nucleic acid into the cytoplasm of the cell. Alternatively peptides or polymers may be used to form complexes with the nucleic acid which may condense as well as protect the therapeutic material as it attempts to reach its target destination. These two approaches are combined in the use of LPD complexes which use a polymer to condense the nucleic acid and a lipid coat to aid entry to the cell.

Introduction

Genetic disorders affect about one in every ten people. Some, like cystic fibrosis, can have consequences early in a child's life while others, like Huntington's disease don't show up until later in life. Preventing genetic disorders can be difficult. Unlike regular diseases which are a result of external factors, genetic diseases are caused by our very own DNA. When the genetic code in a gene is altered, the gene can become defective. Genetic disorders are hereditary. When the defective gene is passed onto an offspring, there is a 50 % risk that that offspring will develop that genetic disorder. Some genetic disorders are caused by dominant genes, requiring only a single gene for the disease to develop. Others are caused by recessive genes which require two copies of the defective gene, one from each parent, to cause the disease. There is a new new technique called gene therapy aimed at treating and curing genetic disorders using drugs or other methods. It involves replacing defective genes with copies of the correct genes. Somatic gene therapy is used to treat people with existing genetic disorders. Germline gene therapy is used to insert corrected genes into the reproductive cells so that future offspring will not contain the defective genes of the parent. Now on to cloning. The dictionary says cloning is the technique of producing a genetically identical duplicate of an organism. A clone is said to be all descendants derived asexually from a single individual, as by cuttings, bulbs, by fission, by mitosis, or by parthenogenesis reproduction. Here are some examples of organisms that have, do, and will continue to clone: Bacteria-Spider, Most Unicellular