Q.For effective treatment of a disease, early diagnosis and understanding its pathophysiology is very important. Early detection is possible through molecular diagnosis. Explain three molecular diagnostic tools for the early detection of disease.

Because conventional diagnosis based on symptoms only becomes possible once the pathogen load is already high, molecular diagnostic techniques — PCR, ELISA, and DNA/RNA probe hybridization — allow detection of a pathogen or a disease-causing mutation at a much earlier, low-concentration stage.

Recombinant DNA technology has provided several molecular tools that allow diseases to be diagnosed at a very early stage, before symptoms even appear, by directly detecting the pathogen's nucleic acid or an antigen/antibody associated with it:

1. Polymerase Chain Reaction (PCR): PCR can amplify even a single copy or a very small quantity of a pathogen's specific nucleic acid (DNA/RNA) into millions of copies, making it detectable. Because it can pick up an infection when the pathogen is still present in very low, otherwise-undetectable amounts, it enables very early diagnosis — used, for example, to detect HIV in suspected AIDS patients, and mutated genes (oncogenes) in cancer patients.

2. Enzyme-Linked Immunosorbent Assay (ELISA): based on the principle of antigen–antibody interaction, ELISA can detect either the presence of a pathogen's antigen or the antibodies produced by the host's immune system in response to infection. It is widely used, for instance, in diagnosing HIV infection.

   …