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• In first step of gene therapy, lymphocytes from the blood of the patient are grown in a
culture outside the body.
• A functional ADA cDNA (using a retroviral vector) is then introduced into these
lymphocytes, which are subsequently returned to the patient.
• As these cells are not immortal, the patient requires periodic infusion of such genetically
engineered lymphocytes.
• If the gene isolated from bone marrow cells producing ADA is introduced into cells at early
embryonic stages, it could be a permanent cure.
• Some other’diseases that can be treated by gene therapy are haemophilia, cystic fibrosis,
Parkinson’s disease, etc.
IV. Molecular diagnosis helps to solve the problem of early diagnosis and treatment of
diseases.
(a) Using conventional methods of diagnosis (serum and urine analysis), early detection of
diseases is not possible.
(b) To overcome this problem, some molecular diagnosis techniques were developed that
provide early detection of diseases. These are as follows:
• Polymerase Chain Reaction (PCR) helps in early detection of diseases or pathogens by the
amplification of their nucleic acid.
Low concentration of pathogens (bacteria, viruses, etc) in the blood does not allow its
detection.
PCR can amplify nucleic acids of such pathogens even when their concentration is very low.
PCR technique can be used for detecting HIV in suspected AIDS patients, genetic mutation
in suspected cancer patients and in identifying genetic disorders.
• Recombinant DNA technology is a modern molecular diagnostic technique. It is done in
the following steps:
A single stranded DNA or RNA tagged with a radioactive molecule called probe, is allowed to
hybridise to its complementary DNA in a clone of cells.
The cells are then detected by autoradiography.
The clone having mutated gene will not appear on the photographic film, because the probe
will not have complementarity with the mutated gene.
• Enzyme Linked Immuno Sorbent Assay (ELISA) is based on the principle of antigen-
antibody interaction. Infection by pathogen can be detected by the presence of antigens
(proteins, glycoproteins, etc) or by detecting the antibodies synthesised against the
pathogen.