He was commenting on a survey begun this year by him and neurologists at Prince of Wales Hospital, United Christian Hospital and Alice Ho Miu Ling Nethersole Hospital, in which samples from Parkinson's disease patients were sent to laboratories in Australia for testing. Among hundreds of patients tested, 34 were aged 45 or less.

Parkinson's disease is commonly caused by deterioration of brain cells in old age, but the genetic form can strike patients even in their teens.

The survey found five patients with mutations in their parkin genes, the most common genetic cause of the disease, and five others who could have the mutation. Hundreds of others had other mutations.

Dr Ng said Asia had a higher proportion of genetic Parkinson's cases than elsewhere, but no explanation for this had yet been found. He declined to say whether Hong Kong's proportion was higher or lower than the world average.

Parkinson's disease occurs when about 80 per cent of the neurons in a part of the brain called the substantia nigra stop producing a chemical, dopamine, key to motor abilities.

Usually they stop functioning in old age, but patients with what is known as autosomal recessive juvenile Parkinson's disease possess a mutated parkin gene that for unknown reasons disrupts the dopamine supply to the brain.

Both parents of patients with this genetic form of Parkinson's likely possess one abnormal parkin gene. Their offspring have a one in four chance of possessing a full pair of the abnormal genes, which leads to the condition. Symptoms manifest themselves before the age of 45.

The genetic form of Parkinson's can take a heavier toll on patients. 'Because they have the disease at a very young age, when they become older, they will have a more severe form,' Dr Ng said. Since symptoms appeared when victims were still of working age, it affected their careers.

Many patients developed fluctuations in their motor abilities after having taken medication for some time. 'So the effectiveness of the drugs becomes less predictable, and involuntary movement becomes more pronounced,' Dr Ng said.

Like other Parkinson's disease patients, those with the genetic form take dopamine agonists, which activate dopamine receptors, and levodopa, which the brain converts to dopamine and which neurologists consider the gold standard in Parkinson's disease drugs.

Dr Ng believes better treatment and more Parkinson's disease genes can be found, but Hong Kong does not have the facilities. Chief Executive Donald Tsang Yam-kuen included a science institute for neurological disease in his last policy address. Dr Ng hopes this centre can attract medical neurologists, neurosurgeons, pathologists and radiologists to research Parkinson's disease genes.