Trials and errors

Genes are the basic units of heredity. They guide the production of proteins, which perform most life functions in our bodies. When alterations in genes render proteins unable to perform their functions, genetic disorders can result. These disorders can be corrected by at least four methods. In the first, a normal gene is inserted into a nonspecific location within the genome to replace a nonfunctional gene. In the second, an abnormal gene is swapped for a normal one through homologous recombination, also known as DNA crossover. In the third, the irregular gene is repaired by selective reverse mutation, which restores normal functionality. In the fourth, the mechanism that turns the affected gene on and off is regulated for the desired result.

In most studies conducted so far, the first method has been used, that is, a normal gene has been inserted into a defective genome. A carrier molecule – a ‘vector’ – is needed in this endeavour to deliver the rectifying gene to the patient’s cells. The vector has in most cases been a virus (adenoviruses and retroviruses being the commonest), although the direct insertion of DNA (or more rarely RNA) and liposomes as carriers have also been used.