Scientists implant human chromosome in mice

By Patricia Reaney

LONDON (Reuters) – Scientists have transplanted a nearly
entire human chromosome in mice in a medical and technical
breakthrough that could reveal new insights into Down’s
syndrome and other disorders.

The genetically engineered mice carry a copy of the human
chromosome 21. It is the smallest of the 23 pairs of human
chromosomes with about 225 genes.

Children suffering from Down’s syndrome, which is one of
the most common genetic disorders, inherit three copies of the
chromosome instead of two.

The achievement caps 13 years of research by scientists at
the National Institute for Medical Health in London and the
Institute of Neurology.

“We are very optimistic that we will be able to get
insights into what goes wrong with people with Down’s,” said Dr
Victor Tybulewicz, who headed the research team.

Down’s syndrome, which affects about one in every 800 live
births, causes delays in mental and physical development.
People with the condition may also have heart defects, hearing
problems and have a higher risk of suffering from leukemia and
early-onset Alzheimer’s disease.

“These disorders that people with Down’s are more prone to
get are ones that also affect all humans. It is entirely
possible that if we gain insights into what is going wrong in
the Down’s syndrome people we will also gain insights into what
goes wrong during those disorders amongst the rest of us,” he
added.

MATCHING GENES TO DISORDERS

Dr Elizabeth Fisher, of the Institute of Neurology, said
the technology will help scientists tease out the genes that
cause the different aspects of Down’s syndrome and
susceptibility to other diseases.

“We believe this new technology will help us work out why
this is, and what to do about it,” she said.

In research reported in the journal Science, the
researchers described how they removed the chromosome from
human cells. Chromosomes are found in the nucleus of a cell and
contain the genes.

The human chromosome was mixed with mouse embryonic stem
cells and a chemical was added that caused them to fuse. The
stem cells that absorbed chromosome 21 were then injected into
mouse embryo which was re-implanted into the mother. The
resulting mouse has a copy of the human chromosome.

Although the mice look normal, they show various features
associated with Down’s syndrome.

The Down’s Syndrome Association in Britain welcomed the
research, saying it could have a positive impact on the lives
of people with the condition.

“Any research that could lead to a greater understanding of
why people with Down’s syndrome are more susceptible to certain
medical conditions is obviously extremely important, although
it must be recognized that this research does not herald a
‘cure’ or a ‘treatment’ for Down’s syndrome,” the association
said in a statement.

But Human Genetics Alert, an independent watchdog that
focuses on the ethics of human genetics, described the
breakthrough as frightening because animals with human genes
are being created.

“It is worrying that there has been no public debate about
whether this kind of technique ought to be allowed. I think we
need a lot more public debate about that,” Dr David King told
Reuters.