Patients with Parkinson's disease could have stem cells injected into their brains to replace damage nerves and restore movement as early as next year, following successful trials in monkeys.

A team of Japanese scientists made the prediction after successfully restoring nerve cells destroyed by a similar condition in primates.

The animals, suffering an artificially induced version of the disease, showed significant improvement two years after having precursor dopamine neurons derived from human stem cells transplanted into their brains.

Charities said if the effect could be replicated in humans it would be 'a groundbreaking feat.'

In humans Parkinson's causes progressive loss of the neurons, which release the vital nerve transmitter chemical dopamine necessary for controlling body movement.

The scientists say they are now just a short step away from testing the treatment, based on laboratory-made stem cells called induced pluripotent stem (iPS) cells, in clinical trials. They hope to start looking for suitable patients within the next 15 months.