News Home » The problems with prenatal testing for autism

Around the World

The problems with prenatal testing for autism

admin 16 Aug 14

When Maureen Bennie’s son, Marc, was 10 months old, he started missing developmental milestones. He had had feeding problems since birth and developed a sleep disorder — and Bennie quickly grew concerned. “I had friends who had children around the same time,” she says. “He really was a very, very different baby in all regards.”

Bennie took Marc to see a doctor but did not come home with a clear diagnosis. And when she got pregnant again when Marc was 17 months old, it didn’t cross her mind that the child she was carrying might face similar challenges. Marc’s autism diagnosis was confirmed when he was almost 3. His baby sister, Julia, was diagnosed about a year later at 23 months. “You just can’t believe it’s happening the second time around. You think: what are the chances?” says Bennie, who later founded the Autism Awareness Centre Inc, a company based in Canada.

Bennie wasn’t aware then that autism frequently recurs in families: Baby siblings of autistic children are about 20 times more likely than the general population to be diagnosed with the condition. Bennie’s children were born in the 1990s, and it wasn’t until the following decade that scientists learned about baby siblings’ high odds. Had Bennie known that Marc has autism before her second pregnancy, she says, she might have avoided getting pregnant again.

These days, with easy access to the facts about autism’s recurrence and, increasingly, to tests that can detect some mutations associated with autism in fetuses, parents like Bennie are facing difficult decisions. Some parents see any knowledge about their unborn child as a bonus, and they welcome the opportunity to prepare for a child on the spectrum — and perhaps to begin therapies early. But others may worry they are ill-equipped to take on the responsibility of raising a child with developmental challenges. They may decide to have fewer children after having a child with autism or even to terminate a pregnancy based on the results of a prenatal test. In surveys, women describe these decisions as “tortured” and talk about a “frenzied search” for more information.

For now, though, the decisions are not based on solid facts: The information prenatal screens such as ultrasounds provide about autism is incomplete and can only hint at a heightened risk. One 2016 study, for example, linked kidney abnormalities on an ultrasound to the possible presence of microdeletions in 17q12, a chromosomal region linked to autism. Another study, published earlier this year, found links between excess brain fluid and mutations in SCN2A, a leading autism gene. Neither of these associations has been proven, however, so these parents should seek confirmation with tests that detect mutations, says Ronald Wapner, director of reproductive genetics at Columbia University‘s Institute for Genomic Medicine, who led the brain-fluid study. “Nobody should make a decision based on just a screening test; they should all have the diagnostic test,” he says.

Diagnostic tests too, though, are less than definitive because researchers are still trying to understand how any given mutation might lead to autism. “Most autism is probably polygenic, meaning there are many, many genes contributing to it,” says Neil Risch, a genetic epidemiologist at the University of California, San Francisco. Even if two people carry the same genetic variant, “one may have a very severe syndrome and the other much milder — or no syndrome at all,” he says. Some parents report feeling “even more uninformed” after chromosomal microarray testing, which can detect some variants linked to autism, he says.

Expectant parents can opt to sequence the whole genome of the fetus, obtained through invasive procedures such as amniocentesis or chorionic villus sampling, or via noninvasive prenatal testing. Most invasive procedures require doctors to insert long needles into a pregnant woman’s abdomen to obtain genetic material from the fetus — and so they raise the risk of miscarriage. By contrast, nonivastive tests need only a simple blood draw from the mother and pose no risk to the fetus.

For now, the question of which technique to use to sample fetal DNA is moot because the American College of Obstetricians and Gynecologists does not recommend whole-genome sequencing for prenatal diagnoses, other than for research purposes. Plus, “it’s expensive and it takes time, and specialized people are needed for interpretation,” says Diana Bianchi, director of the Eunice Kennedy Shriver National Institute of Child Health and Human Development. However, genome sequencing is likely to become more common as its cost drops and more people gain access to noninvasive tests.

When that happens, experts warn, it is likely to bring with it a host of thorny issues. Some say the tests may lead to more terminations — to the detriment of a society’s neurodiversity. In Iceland, for example, only about two children with Down syndrome have been born each year since the introduction of prenatal tests for the syndrome in the early 2000s.

The more sensitive prenatal tests for autism become, the more likely they are to present families with increasingly challenging dilemmas. “What should we test for? What should we not test for?” Wapner says. “As our tools get better, these questions become more important; that’s all worthy of a very difficult discussion.”