Scientists have successfully eased some of the symptoms of a Down's-like condition in mice by injecting protein during pregnancy.
The results have raised the hope of treating unborn babies known to have the incurable genetic condition.
However, it would have to pass rigorous safety tests before being accepted for widespread use. There are also likely to be ethical concerns.
The research centred on two proteins that help brain cells develop. People with Down's produce fewer of these proteins.
The American scientists, from the National Institutes of Health in Maryland, injected the proteins into mice pregnant with pups that had been genetically engineered to have a Down's-like condition.
When the pups were born, they reached developmental milestones at the same time as normal mice, this week's New Scientist reports.
The researchers are waiting to see if the benefits are long lasting.
They said they were cautiously optimistic about their work but warned that what works in mice or in the lab doesn't always work in people.
Any tests on humans would be still some years away.
Carol Boys, chief executive of the Down's Syndrome Association, said: "We welcome research that may have a positive impact on people with Down's syndrome.
"However, it must be recognised that this research doesn't herald a 'cure' or 'treatment' for Down's syndrome. We'll be following how it develops with great interest."
