The abnormalities in question are called trophoblast inclusions, or TIs. They are created when the placenta doesn't develop properly, and they are a marker for various genetic abnormalities. When a placental sample is examined on a slide under a microscope, TIs appear as dark blobs.
Dr. Harvey Kliman came up with the hypothesis that TIs might be linked to autism after he was asked to examine two placentas with many abnormalities. It turned out those placentas belonged to children with autism.
To see whether his inkling had any merit, Kliman, a research scientist in obstetrics, gynecology and reproductive sciences at the Yale School of Medicine, found 13 children with an autism spectrum disorder and 154 children who didn't. Then he compared samples from their placentas and found that TIs occurred three times more often when children had an ASD. He and his colleagues reported those results in 2007.
The new study was more ambitious. Kliman teamed up with researchers from the UC Davis MIND Institute. They found 117 pregnant women who already had a child with autism and thus were more likely to have another child with the disorder. The placentas from these high-risk pregnancies were compared with placentas from 100 women who had no heightened risk of having a baby with autism.
It turned out there was a marked difference in TIs between the two groups. A full 92 percent of the control placentas had no TIs whatsoever, and none of them had more than two TIs.
On the other hand, placentas from the high-risk pregnancies had as many as 15 TIs. Only 59 percent of placentas had none. That meant that if the researchers found two or more TIs in a patient's sample, the odds that the baby would have autism increased by a factor of 8.
Then the researchers ran the numbers again, this time using only the high-risk women who were most similar to the women in the control group. In this comparison, the presence of two or more TIs meant the risk of autism increased by a factor of 11.5.
The results were published Thursday in the journal Biological Psychiatry.
The test can't say whether a particular infant will grow up to develop autism. At best, it can only serve as a warning that a particular baby has an increased risk of developing autism.
Still, that information could be tremendously useful to parents. Research suggests the sooner parents can begin performing behavioral interventions -- eye contact exercises, for instance, and using children's names -- the more their autism symptoms will fade.
"Practice guidelines from the American Academy of Pediatrics recommend that all children undergo screening for autism at 18 months of age, by which time a considerable amount of neurological plasticity and opportunities for intervention to maximize outcome has been lost," the research team wrote. The placental test is appealing because it provides a way to screen for risk in plenty of time to give parents a chance to do something about it.
The recommended intervention is actually good for all parents, Kliman said. "The beauty of it is that the intervention is attentive parenting, with increased stimulation and physical contact," Kliman said. "I call this attentive parenting. It's like Baby Einstein times two."
The researchers haven't put their test to the test in real-world conditions. That would involve examining the placentas of every baby born in a single hospital during a set period of time, waiting five to 10 years to see how many of those kids wound up with an ASD, then checking to see whether the TI test did a good job of predicting which kids developed autism and which ones didn't.
Realistically, the chances of anyone conducting that kind of trial are slim to none, Kliman said. "No one is going to fund that," he said. "That is just not going to happen."
But as a clinician, Kliman said he wouldn't hesitate to use this test on his patients. "This is better than most clinical tests we have right now," he said. "It's better than the PSA test for prostate cancer. CA-125 is a terrible test for ovarian cancer and we use it all the time."
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