London - The first steps towards genetic therapy for Down's syndrome children have been taken in a study showing that it is possible to turn off the entire extra chromosome in the cells of people suffering from the condition.
It is the first time that scientists have been able to switch off a complete human chromosome, which could lead to a greater understanding of what goes wrong when babies inherit three copies of a chromosome rather than the usual two, the researchers explained.
Down's syndrome, the most common chromosome defect, results in serious developmental abnormalities and a shorter life expectancy.
It usually occurs when an embryo inherits three copies of chromosome No 21 - one of the 23 pairs of human chromosomes - but correcting this major inherited defect with gene therapy was considered to be too complex and difficult. However, working on stem cells derived from a patient with Down's syndrome, scientists have been able to insert a genetic switch into the extra, third chromosome.
This switch, called the Xist gene, normally turns off the second X chromosome found in the cells of women so that only one X chromosome actually functions, as it does in men.