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.

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