Explain gene therapy, with reference to treatment of SCID.

Explanation

Gene therapy is an experimental technique in which genes are introduced into individual cells or tissues, to cure some hereditary diseases in which a defective allele of a gene is replaced with normal one. Deficiency of Adenosine Deaminase causes SCID. The technique of gene therapy was initiated in 1972. Severe Combined Immune Deficiency (SCID) is a potentially fatal primary immuno deficiency in which there is combined absence of T-lymphocyte and B-lymphocyte function. There are at least 13 different genetic defects that can cause SCID. These defects lead to extreme susceptibility to very serious infections. This condition is generally considered to be the most serious of the primary immune deficiencies. From the bone marrow of the patient are cultured outside the body. The functional ADA gene is transferred into these cells through the use of restriction enzymes. Another type of SCID is caused by mutations in a gene that encodes an enzyme called adenosine deaminase (ADA). ADA is essential for the metabolic function of a variety of body cells but especially T-cells. The absence of this enzyme leads to an accumulation of toxic metabolic byproducts within lymphocytes that cause the cells to die. For patients with SCID due to ADA deficiency, replacement therapy with a modified form of the enzyme (from a cow, called PEGADA) has been used with some success. Transformed cells are transferred to the patient, T cells and B Cells appear in the blood.