Yahoo – AFP,
16 April 2014
AFP/File - Children with Down's syndrome play on March 17, 2011 at an activity center in Moscow |
The extra
copy of Chromosome 21 that causes Down's syndrome throws a spanner into the
workings of all the other chromosomes as well, said a study published Wednesday
that surprised its authors.
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.
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."
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.
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