Researchers have based their claims on an experiment on rodents – they injected two key proteins (the nerve cells of which are starved by Down's syndrome, leading to problems with mental development) into pregnant mice with Down's pups and found the offspring to be free of these problems.

Down's syndrome in humans is caused in children who inherit an extra copy of one of the body's chromosomes – bundles of genetic material which help control how people develop and live.

In fact, in their study, the researchers at National Institutes of Health in Maryland injected the proteins – NAP and SAL – into mice pregnant with trisomic pups in the middle of their pregnancy.

When the pups were born, they reached developmental milestones such as grasping a rod, righting themselves and responding to tactile stimulation at the same time as normal mice, the study revealed.

"We were able to prevent a significant amount of the delay," the 'New Scientist' quoted lead researcher Catherine Spong as saying.

Moreover, the brains of the treated mice showed normal levels of ADNP – one of the regulatory proteins under-produced by Down's-affected glial cells – and of another compound that is a marker for healthy glial cells.