Epilepsy patients should take genetic test: HSA

SINGAPORE - Local epilepsy patients are now being told to take a genetic test which may save their lives.

The test detects whether a patient has a genetic predisposition to possibly fatal skin reactions after taking carbamazepine, a drug commonly given to epileptics.

This is the first time here that genetic screening is being "highly recommended" for a drug, after the health authorities investigated the problem among the local population.

It may pave the way for more personalised care in other diseases, said Ms Dorothy Toh, director of the Health Sciences Authority's (HSA) vigilance branch.

About one in 100 people has epilepsy, a nerve disorder marked by sudden seizures. To control the incurable disease, carbamazepine - available here since 1988 and also used to treat other nerve-related ailments like bipolar disorder - is the drug of choice.

But the drug has also caused two life-threatening skin reactions, Stevens-Johnson syndrome and toxic epidermal necrolysis, among patients here over the past decade. These involve burn-like rashes and painful ulcers.

Last year, about 80 cases of the two conditions were reported, after a high of 110 in 2010.

In 2009, HSA, three public hospitals and other agencies began investigating.

They found the reactions were linked to the presence of the HLA-B*1502 genetic variation in local patients. Singapore Immunology Network data also showed the HLA-B*1502 allele is most common among Malays here, a fifth of whom carry it.

On April 30, HSA urged doctors to send new patients for a test to detect the allele. A letter issued with the Health Ministry states that genotype testing before prescribing carbamazepine is now the new standard of care.

The test costs about $190 but may be subsidised to about $50. It takes about two to four days for a result. Those testing positive can then be given alternative drugs.

Patients on the drug for more than three months without problems do not have to be tested.

A 44-year-old who had Stevens- Johnson syndrome in 2003 after taking carbamazepine for a nerve injury, feels the genetic test will help. He was in a brief coma within days of falling ill, his skin blackened and sores developed.

"Doctors asked my mother to prepare for the worst," he recalled. "All doctors prescribing carbamazepine should ask their patients to do this test."

One in 20 people who get Stevens- Johnson syndrome dies.

So far, no adverse skin reactions linked to carbamazepine have been reported since the new standards kicked in, said Ms Toh.

"Moving forward, this will change the way doctors prescribe medicine to their patients."

But she said establishing a link between genes and drug safety is a long and complicated process. Multiple genes can influence the way a person responds to a drug.

Professor Edmund Lee, from the National University of Singapore's pharmacology department, was involved in the HSA investigation and said this is a good first step towards personalised health care. But there is still a long way to go, especially to find links between genes and drugs.

"For the genetic platform to show its true colours, it requires a lot of validation," he said.


Get a copy of The Straits Times or go to straitstimes.com for more stories.