Adenosine deaminase is a mammalian enzyme which acts as a catalyst during the conversion of adenosine to the nucleotide inosine. This conversion takes place through the removal of an amino group. The deficiency of this enzyme cause genetic/inherited diseases.

Deficiency of Adenosine Deaminase:-
The deficiency of adenosine deaminase affects the immune system of the individual and is the cause of genetic disorder that is called as Severe Combined Immunodeficiency. People mainly children who have this deficiency, they can easily get affected to all the microorganisms like bacteria, viruses and fungi due to their weak immune system. Sometimes the infections due to these microorganisms become so severe that they can cause death of the children. Some diseases like diarrhea, pneumonia and malaria which affect the people with season, children of weak immune system get infections very often.

The disease of SCID occurs in very few children and is not a very common disease. The adenosine deaminase enzyme is produced by the coding of the ADA gene. This enzyme is present in almost all the tissues. The lymphocyte development takes place through this enzyme. Lymphocyte cells are the white blood cells which are the main components of immune system and they make antibodies. Either they fight against various viral infections or make the immune system so strong that it itself protects the body against diseases. But the children who lack this enzyme or if this enzyme is produced in very low amount, then the immune system of the children cannot protect the body against infections.

Treatment of ADA deficiency with gene Therapy:-
For treating the child with gene therapy, and for the safety of the child's life, it is necessary to keep the child in a sterilized environment. The food he eats o the water he drinks, all should be sterilized. During the treatment, the gene of interest that is ADA, is taken out of the body and is cloned in the laboratory under specific conditions. The cloned gene is inserted in those cells which have the ability to live long. For this purpose, it would be better if the patient's own cells are used. These cells are grown using tissue culture techniques and then are inserted back in the body of the patient. The cloned genes are inserted into the DNA in the special cells so that the desired gene can undergo the processes of transcription and translation. These processes enable the genes to produce adequate amounts of the ADA enzymes. The source for inserting the cloned gene into the DNA is retrovirus which is the best vector and can efficiently insert the genes into human cells. There are two reasons for which these viruses are used as vectors because the envelop proteins of viral cell wall have the ability to infect human cells and the other reason is that the RNA of the ADA gene can easily combine with the viral genome. The commonly used cells for SCID treatment are the T-cells which can be grown in the tissue culture.

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