What is a gene?
The hereditary units which are transmitted from one generation to the other are called genes. A gene is the fundamental unit like atom is the fundamental physical unit.
Classically, a gene was assumes to be a genetic unit by the following criteria:
1. A gene is a unit of physiological function that occupies a definite location in the chromosome and is responsible for the expression of the phenotypic character like the wings ,color of eyes etc.
2. A gene is the unit of transmission or segregation because it is segregated and exchanged at the time of meiosis.
3. It is a unit of mutation, because by a spontaneous induced change a different phenotypic character is expressed.
Because of the defects in the genes many diseases are caused which sometimes have no much cure. Later a technique of gene therapy was introduced for correcting defective genes responsible for disease development. The process is carried by any of the following methods;
Gene therapy is the insertion, alteration, or removal of genes within an individual's cells and biological tissues to treat disease. Following approaches can be made in gene therapy
• A defective gene could be exchanged for a normal gene through homologous recombination.
• The nonstandard 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.
• Introducing a new gene into the body to help fight a disease.
TYPES OF GENE THERAPY
Gene therapy may be classified into the two following types:
Germ line gene therapy
In this, Germ cells, i.e., sperm or eggs are tailored by the introduction of well-designed genes, which are incorporated into their genomes. After the insertion the characters of the gene would be heritable and would be passed on to later generations. This approach is highly effective in fighting genetic disorders and hereditary diseases.
Somatic gene therapy
In the case of somatic gene therapy, the remedial genes are shifted into the somatic cells of a patient. Any modifications and effects will be limited to the individual patient only, and will not be inherited by the patient's offspring or later generations
HOW DOES GENE THERAPY WORK?
A gene cannot be directly inserted into a person's cell. It must be transported to the cell using a carrier, or vector. Vector systems can be divided into:
• Viral Vectors
• Non-viral Vectors
In gene therapy 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 deliver 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.
Defective cells are infected with the viral vector, which releases the genetic material containing the curative human gene into the defective cell. The generation of a functional protein product from the therapeutic gene restores the defective cell to a standard state.
• Retroviruses - 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.
• Adenoviruses - 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.
• Adeno-associated viruses - A class of small, single-stranded DNA viruses that can insert their genetic material at a specific site on chromosome 19.
• Herpes simplex viruses - 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.
There are several no viral options for gene delivery. The uncomplicated method is the direct introduction of therapeutic DNA into aimed cells. This approach has its disadvantage 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 defective cell's membrane.
Other way is done chemically linking the DNA to a molecule that will bind to special cell receptors. Once bound to these receptors, the curative DNA are swallowed up by the cell membrane and passed into the interior of the target cell.
ADVANTAGES OF GENE THERAPY
It is not always successful yet disease can be eradicated for a person and their future offspring, so it is a remedy not just one generation but also in succeeding generations. . For example, a baby just born can undergo gene therapy in the womb to remove the breast cancer gene, as both parents had strong family histories of the cancer. As a result, unless the child is exposed to lots of carcinogens, child has no chance of developing the cancer. This is one of many cases where a genetic illness has been virtually eradicated.
Gene therapy has the potential to eliminate and prevent hereditary diseases such as cystic fibrosis and is a possible cure for heart disease, AIDS and cancer. Genetic disease can be cured by replacing non-functional gene with a functional one. This may give someone a chance of normal life.
Gene therapy can 'silence' a gene. In the case of someone with HIV, which had not yet developed into AIDS, scientists could save them the pain and suffering of the disease by using gene therapy to 'silence' the disease before its onset.
DISADVANTAGES OF GENE THERAPY
• Short-lived nature of gene therapy which makes the patients to undergo multiple rounds of gene therapy.
• Immune response is of stimulated that reduces gene therapy effectiveness which is always a potential risk.
• Problems with viral vectors - Viruses, which is used as vehicles in most gene therapy present a variety of potential problems to the patient --toxicity, immune and inflammatory responses, and gene control and targeting issues. In addition, there is always the fear that the viral vector, once inside the patient, may recover its ability to cause disease.
• Multigene disorders, such as heart disease, high blood pressure, Alzheimer's disease, arthritis, and diabetes, are caused by the combined effects of variations in many genes. Multigame disorders such as these would be especially difficult to treat effectively using gene therapy.
• Also, there are a few side effects. These include nausea and temporary drowsiness.
• For the diagnosis of disease in a fetus or embryo before it is born prenatal testing is performed. If an unborn carries any defective gene then their parent's definitely want to abort this child this may increase number of abortions. This is major disadvantage of gene therapy. This creates many ethical problems.
As gene therapy is uprising in the field of medicine. In the near future, every genetic disease will have gene therapy as its treatment. Gene therapy could be last cure for every genetic disease. Overcoming all its hurdles it would change our lives forever.
About Author / Additional Info:
I have done biotech in my under graduation and it interests me still.