Little Grayson Spencer can’t talk, can’t walk and may never learn how – but baffled doctors admit they don’t know why.

He looks like any happy three-year-old rolling around on his tricycle and hugging his parents tightly.

But his life has been far from ordinary.

Grayson, of George Roche Road, Canterbury, was born with brain damage and later developed a genetic condition so rare doctors have been unable to diagnose it.

Parents Kara, 31, and Ashley, 35, have revealed the heartbreak of their son’s undiagnosed condition, which leaves them unable to communicate with their little boy.

Kara said: “It is a very lonely life. Grayson requires 24-hour care, but a lot of it is guesswork because he can’t tell us when he is hungry or thirsty.

“He has learned to eyedart to tell us when he wants something and we leave cups around the house so he can tell us when he is thirsty.

“It is hard to explain to people. Because the condition doesn’t have a diagnosis people seem to think we’re making it up. He looks like a normal little boy but kids don’t understand he doesn’t play, he doesn’t talk.

“Very few charities can help me because it doesn’t have a name. We don’t get the same support network. There is a Facebook group with about 500 of us but that is it.”

Grayson is one of 300 UK children to be tested under a study which uses new technologies to diagnose children’s development disorders.

His parents said it could take up to two years to learn more about their son’s condition.

Kara said her son spent an average of four days a week in hospitals, including Kent and Canterbury and the specialist children’s unit at St Thomas’s in London.

The couple have begun fundraising for the charity SWAN – Syndrome Without A Name – and are campaigning for undiagnosed conditions to be treated like other disabilities.

They recently raised enough money to buy a tricycle for Grayson, which helps him move around and strengthen his muscles, and on Saturday Kara shaved off her hair to collect £2,800 for child cancer sufferers.