Research Says Down's Chromosome Causes Genome-Wide Disruption

A new study has found that the extra copy of Chromosome 21 that causes Down's syndrome throws a spanner into the workings of all the other chromosomes as well.

Using data from a set of twins, one with Down's and one without, researchers found a major difference in how genes functioned between the two.

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The twins were born from a single egg that split, which means their DNA code started off identical.

But the individual with Down's had an extra copy of Chromosome 21 -- a difference enabling the scientists to see how this might affect the same genome.

The additional chromosome had a knock-on effect on all the 22 other chromosomes, the team reported in the journal Nature.

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"We were very surprised by this finding," said Audrey Letourneau of the University of Geneva Medical School who co-authored the study.

"It seems that this small, extra chromosome has a major influence on the entirety of the genome."

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Chromosomes are made up of bundles of DNA called genes, which hold the information for cell function.

Humans have 23 pairs of chromosomes-- or a total of 46 per cell.

People with Down's Syndrome, about one in every 750, have a third, extra Chromosome 21 -- the smallest of all the chromosomes with about one percent of the DNA in a cell.

Down's is the world's leading genetically-caused mental disease, and also carries a heightened risk of heart defects, leukaemia, immune-system malfunction and premature Alzheimer's disease.

The results may help researchers "find substances that could reverse this gene-expression dysregulation, i.e. drugs that revert the expression of genes... back to normal," co-author Stylianos Antonarakis told AFP.

Source-AFP