Led by Dr Verayuth Praphanphoj of the Rajanukul Institute, the research team looked into a specific region of chromosomes of about 200 children born with unexplainable mental retardation to find a genetic abnormality called "cryptic subtelomeric re-arrangement".

Previous foreign studies found this genetic abnormality was attributed to between 7 and 10 per cent of children's mental retardation with an unknown origin, said Verayuth.

It was found that 10 out of those 200 cases had the genetic abnormality, accounting for 5 per cent, which was close to the percentage found in the western research.

This research took three years to complete and was funded by Biotec.

Compared to the general chromosome screening used widely to test for potential carrying of certain inherited diseases, Subtelomeric FISH was much more specific, Verayuth said.

"While the former is like an X-ray, the latter is like a CT or MRT scan and is sophisticated enough to show the exact details of what we're looking for," he added.

The new test will also benefit children born with multi-congenital abnormalities because cryptic subtelomeric re-arrangement may also be responsible for this type of severe birth defect.

"If you have a child who appears normal yet has problems in study performance, this testing method will show that one of his chromosomes is abnormal, thus you have to think twice about planning to have another baby," said Dr Somchai Chakrabhan, the director-general of the Department of Mental Health.

The development of this method was applied from the one used in the West, but was Bt10,000 cheaper, said the doctor, adding the cost of the new test will still be about Bt30,000.

"This is a step forward to improve the diagnosis of neurological and mental diseases caused by genetic factors," said Dr Panpimol Lotrakul, the director of Rajanukul.

Arthit Khwankhom

The Nation