After Madam Phoebe Yang discovered that her 13-year-old son was autistic, she feared that if she had another child, that sibling would acquire the disability, too.
Not knowing if the autism had a genetic cause burdened the 48-year-old designer. But perhaps it will not trouble others in a similar situation much longer.
In what is a breakthrough in the field of genetics, a Singaporean doctor has developed a method to detect disease-causing gene mutations that lurk in only a tiny fraction of the body's cells, making them hard to find.
Known as somatic mutations, these can cause diseases from autism to schizophrenia, but cannot be detected using standard genome sequencing tests. Importantly, these mutations are not hereditary. If a child has it, it was not inherited from the parents.
This could bring give parents like Madam Yang peace of mind.
Now that doctors can trace these mutations, it means they can reassure parents whose child has these that they can attempt another pregnancy without risk, said Dr Saumya Jamuar, a paediatric geneticist at KK Women's and Children's Hospital.
"This will definitely change the way we counsel patients and their parents... Previously, we would tell them the risk of (having another affected child) is between 2 and 10 per cent, mainly because we didn't have a cause," he said.
Dr Saumya's research was done in collaboration with the Howard Hughes Medical Institute and the Boston Children's Hospital, where he had been a post-doctoral fellow previously.
Their findings were published two weeks ago in the New England Journal of Medicine, considered one of the most prestigious in the world.
The team tested more than 150 patients whose brain abnormalities remained unexplained.
Rather than use standard tests that sample a large set of genes between 30 and 50 times, they sampled a smaller set of selected genes associated with brain abnormalities about 1,000 times. "We didn't look wide. Instead, we looked deeper," said Dr Saumya.
They found somatic mutations in a surprisingly high rate of about one in three patients whose illness was genetically caused. "Previously, they would not have known why they have this disease."
He added that finding a genetic cause would help stop some mothers - especially in Asia - from blaming themselves. Some may have falsely believed that their child's disease was because of, say, their diet during pregnancy.
Dr Saumya is seeking grants to apply his team's method to autistic patients. Every year, 250 to 300 Singaporeans are diagnosed with autism. He hopes the technique can be used here within the next one to two years.
Madam Yang, who knows many parents whose autistic child is their only one, said the research could help reassure them that it is not a given that their next child would also be affected. "Normally for parents who have an autistic child, they don't have the courage to have a second one."