A CLUE to the developmental problems that lead to autism has been found in a study by scientists in the United States.

They compared the placentas from babies who went on to develop autism with those from normal children, and found that a characteristic pattern was three times more common in the former. The team, led by Dr Harvey Kliman of Yale School of Medicine, examined placentas from 13 autistic children and 61 without the disability. In each case, tissue samples from the placentas had been stored at birth.

The abnormality the team was looking for was unusual folding of the surface layers of the placenta, that tends to trap a class of cells called trophoblasts as “inclusions” within the layers. These inclusions can easily be seen by looking at cross sections of the surface layers, mounted as slides, in a microscope.

In normal development, the team hypothesised, such inclusions do not occur; but, when development is abnormal, they do.

In 27 slides from placentas of babies who went on to develop autism, inclusions were found in 6; but in 154 slides from normal babies, only 12 were found. This means that the inclusions were three times as common in autistic babies as in normal ones, the team reports in Biological Psychiatry.

“We knew that trophoblast inclusions were increased in cases of chromosome abnormalities and genetic diseases, but we had no idea whether they would be significantly increased in cases of autism spectrum disorder,” Dr Kliman said.

The test, however, is not specific enough to serve as an early warning of autism. Even in the autistic children, inclusions appeared only in a minority of slides, and they were also found in normal children, albeit in smaller numbers; so using the presence of inclusions as a test would lead to false positives and false negatives.

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