Gene into the genome of the host cell.

Gene therapy is an experimental technique that uses genes to treat or prevent disease. It replaces a faulty gene or adds a new gene in an attempt to cure disease or improve body’s ability to fight diseases. Gene therapy holds promise for treating a wide range of diseases, such as cancer, cystic fibrosis, heart disease, diabetes, hemophilia and AIDS. Researchers are testing several approaches to gene therapy, including:• Replacing a mutated gene that causes disease with a healthy copy of the gene.• Inactivating, or “knocking out,” a mutated gene that is functioning improperly.• Introducing a new gene into the body to help fight a disease.

Gene therapy may be classified into two types:• SomaticIn somatic cell gene therapy (SCGT), the therapeutic genes are transferred into any cell other than a gamete, germ cell, gametocyte, or undifferentiated stem cell. Any such modifications affect the individual patient only, and are not inherited by offspring.  SCGT focus on severe genetic disorders, including immunodeficiencies, hemophilia, thalassaemia, and cystic fibrosis. Such single gene disorders are good candidates for somatic cell therapy.

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 • Germline In germline gene therapy (GGT), germ cells (sperm or egg cells) are modified by the introduction of functional genes into their genomes. Modifying a germ cell causes all the organism’s cells to contain the modified gene. The change is therefore heritable and passed on to later generations. The delivery of DNA into cells can be accomplished by multiple methods. The two major classes are:• Viral methods:In order to replicate, viruses introduce their genetic material into the host cell, tricking the host’s cellular machinery into using it as blueprints for viral proteins. Retroviruses go a stage further by having their genetic material copied into the genome of the host cell.

Scientists exploit this by substituting a virus’s genetic material with therapeutic DNA. A number of viruses have been used for human gene therapy, including retroviruses, adenoviruses, herpes simplex, vaccinia, and adeno-associated virus.• Non-viral methods:Non-viral methods present certain advantages over viral methods, such as large scale production and low host immunogenicity. However, non-viral methods initially produced lower levels of transfection and gene expression, and thus lower therapeutic efficacy.

Later technology remedied this deficiency. Methods for non-viral gene therapy include the injection of naked DNA, electroporation, the gene gun,  the use of oligonucleotides, lipoplexes, dendrimers, and inorganic nanoparticles. Successful cases of gene therapy: ASHANTI DESILVA: The first successful case of       gene therapy occurred in the 1990s on a young girl named Ashanti DE Silva, a victim of the recessive metabolic disorder, ADA deficiency, which made her immune system weak and vulnerable to nearly every virus. She lacked the ability to produce a key enzyme which would ultimately lead to death at a young age. Her doctors took samples of her blood, treating her malfunctioning white blood cells with the genes she did not have. They reinjected the blood back into her with the corrected genes. This treatment did help her to produce the enzyme but it did not help her to make healthy cells. Today, she still has to receive repeats of her gene therapy treatment to stabilize the amount of enzyme in her blood.

  RHYS JONES:  He was born with X-linked SCIDS or Severe combined immunodeficiency, a disease that affects boys, making them lack cells in their immune systems. People with SCIDS have been called “bubble boys” because of their fragile immune systems. Because Jones had no siblings, he had to find healthy marrow from another source. At Great Ormond Street Children’s Hospital in Great Britain, Jones was cured. Doctors removed some of his bone marrow and used a virus to add immune system genes to the cells.

They then reinserted the marrow into Jones. This treatment saved Jone’s life.  Three other people have received the same gene therapy as Jones, and have been cured as well


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