Gene Therapy
A great leap in medical science has taken place on the 14th September 1990, when a girl suffering from adenosine deaminase deficiency (severe immunodeficiency) was treated by transferring the normal gene for adenosine deaminase.
Gene therapy is the introduction of genes into existing cells to prevent or cure a wide range of diseases.
Gene therapy is a technique for correcting defective genes responsible for disease development.
Gene therapy replaces a faulty gene (DNA sequencing) or adds a new gene in an attempt to cure disease.
Genetic modification of cells to produce therapeutic effect or treatment of disease by repairing or reconstructing defective genetic material (DNA sequence, protein sequence, chromosomes).
Gene Therapy Strategies
1. Gene Augmentation theory
A new protein coding gene is inserted into the cell to replace the missing gene product.
Cell with non- functioning gene ----- functioning gene -------- Cell functioning normally
2. Gene inhibition therapy
Suitable for the treatment of infectious diseases, cancer and inherited disease caused by inappropriate gene activity.
The aim is to introduce a gene whose product either;
1. Inhibits the expression of another gene.
2. Interferes with the activity of the product of another gene.
3. Eliminate the activity of a gene that encourage the growth of disease-related cells.
Approaches for Gene Therapy
Two approaches to achieve gene therapy are;
1. Somatic cell gene therapy
2. Germ cell gene therapy
1. Somatic cell gene therapy
The non-reproductive (non-sex) cells of an organism are referred to as somatic cells.
These are the cells of an organism other than sperm or egg cells. For example; Bone marrow cells, blood cells, skin cells, intestinal cells.
Aat present, gene therapy directed to correct the genetic defects in somatic cells.
It involves the insertion of a fully functional and expressible gene into a target somatic cell to correct a genetic disease permanently.
Somatic cell gene therapy aim to cure a disease only in the patient.
2. Germ cell gene therapy
The reproductive (sex cells) of an organism constitute germ cell line.
Gene therapy involving the introduction of DNA into germ cell is passed on to the successive generations.
Ethical and technical reasons, germ cell gene therapy is not being attempted at present.
Types of Gene Therapy
1. Ex-Vivo gene therapy
Involves the transfer of genes in cultured cells (for example; Bone marrow cells) which are then reintroduced into the patient.
2. In-Vivo gene therapy
The direct delivery of genes into the cells of a particular tissue is referred to as In-vivo gene therapy.
Technique of Ex-Vivo gene therapy
1. Isolate cells with genetic defect from the patient.
2. Grow the cells in nature.
3. Introduce the therapeutic gene to correct gene defect.
4. Select the genetically corrected cells and grow.
5. Transplant the modified cells to the patient.
A men with genetic defect ---- Isolated cells ---- Cell culture ---- Therapeutic gene constructs ---- Genetically transformed cells selected ---- Transplantation
(the procedure of Ex-vivo gene therapy)
Vectors in Gene Therapy
1. Viruses; retroviruses
2. Human artificial chromosomes
3. Bone marrow cells
In -Vivo Gene Therapy
1. Direct delivery of the therapeutic gene (DNA) into the target cells of a particular tissue of a patient constitutes in vivo gene therapy.
2. Gene delivery can be carried out by viral or non- viral vector systems.
3. Success of In vivo gene therapy mostly depends on;
1. Efficiency of the uptake of the remedial (therapeutic) gene by the target cells.
2. Intracellular degradation of the gene and its uptake by nucleus.
3. Expression capability of the gene.
Therapeutic gene ---- target tissue
(P- promoter gene specific for therapeutic gene)
Ethical issues Regarding gene therapy
What are criteria of distinguishing "good" and " bad" uses of gene therapy?
Who decide which traits are normal and which constitute a disability or disorder?
Will the costly gene therapy be available only to the wealthy?
Could be wide spread use of gene therapy make society less accepting of people who are different?
Should people be allowed to use gene therapy to enhance basic human traits such as; Height, intelligence, athletic ability.
0 Comments