Narcolepsy is a brain disorder characterised by sleep attacks and abnormal eye movement. It affects up to one in a thousand people.

Suffers fall asleep anywhere, at any time of day without warning.

At other times sufferers remain conscious, but their entire body goes limp and they are unable to move.

The condition impinges on every aspect of life, and can make it difficult for sufferers to hold down jobs, or personal relationships.

Narcolepsy was first described more than 100 years ago, but the cause of this disease is still not known.

Researchers believe it is caused by an interplay between genetic and environmental factors. One identical twin may suffer from the condition, while the other may not.

In most human cases, it takes several years after the disease onset before it is finally diagnosed, and in some cases the problem is ignored or is thought to be a personal problem rather than a medical problem, such as believing that the person is just lazy.

Studies of the condition in dogs have linked it to mutations in a receptor in the brain - the hypocretin 2 receptor - involved in the transmission of nervous impulses.

'Big step forward'

A team from Stanford University have now taken that research one step further by examining levels of a protein involved in the same neural pathway, hypocretin 1, in human narcoleptics. Their work is published in The Lancet medical journal.

They found that seven out of nine individuals with the disorder had undetectable levels of hypocretin 1.

They believe that the cells in the brain secreting hypocretins are destroyed or cannot secrete hypocretins and this produces the symptoms of narcolepsy.