Doctors say they are close to identifying a gene that may explain why Hong Kong people have the highest incidence of colon cancer in the world. Ten families with a history of the disease have been genetically tested and initial findings suggest they share a common gene, said Dr Judy Ho Wai-chu, senior medical officer in the department of surgery at Queen Mary Hospital. If the gene is identified it will help develop a test for Chinese families at risk of developing the cancer and could lead to a drug to alter the defective gene. Dr Ho said preliminary data indicated Chinese may have a specific gene. 'So far we have found one very suggestive gene,' she said. 'That may explain why our incidence of young colon cancer is higher than the rest of the world.' An earlier study at Queen Mary Hospital found the cancer afflicted Hong Kong people aged 30 to 40, among whom it was four times more likely than among people in Scotland, Japan and the white population of the United States. Scientists elsewhere have identified 10 colon cancer genes that lead to the inherited form of the disease. The Hong Kong study is trying to identify which one, or which combination, occurs more frequently and is peculiar to southern Chinese. 'Any population can have any one gene that has a problem, what we call the founder gene - the one that is very abnormal from the very beginning that is peculiar to our ancestors,' Dr Ho said. 'That abnormality obviously got spread within that population.' She said that once the founder gene was located, Chinese families could be tested for that gene. It might also be possible to alter the gene. In 1995 her team set up a registry to provide check-ups and genetic screening for families predisposed to colon cancer. More than 300 families were being monitored, of which 70 were found to have the inherited form of colon cancer.