Which one of the following is NOT a method of molecular diagnosis for early detection of a disease?

RNAi

The correct answer is Option (2) → RNAi

A nematode Meloidegyne incognitia infects the roots of tobacco plants and causes a great reduction in yield. A novel strategy was adopted to prevent this infestation which was based on the process of RNA interference (RNAi).Using Agrobacterium vectors, nematode-specific genes were introduced into the host plant . The introduction of DNA was such that it produced both sense and anti-sense RNA in the host cells. These two RNA’s being complementary to each other formed a double stranded (dsRNA) that initiated RNAi and thus, silenced the specific mRNA of the nematode.

Early diagnosis and understanding the pathophysiology of a disease are crucial for effective treatment. Conventional diagnostic methods, such as serum and urine analysis, may not always lead to early detection. However, modern techniques like Recombinant DNA technology, Polymerase Chain Reaction (PCR), and Enzyme Linked Immuno-sorbent Assay (ELISA) have proven effective in achieving early diagnosis.

Typically, the presence of a pathogen (bacteria, viruses, etc.) is suspected only after disease symptoms have manifested. By this time, the pathogen concentration in the body is already high. However, PCR, a sensitive molecular technique, enables the detection of even low concentrations of pathogens before visible symptoms appear. PCR has become a routine tool in diagnosing HIV in suspected AIDS patients and identifying mutations in genes among suspected cancer patients. Moreover, PCR is a valuable technique for identifying various genetic disorders.

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.