Autistic children differ markedly from healthy volunteers in metabolic compounds shed in their urine, raising hopes for a biological test for the disorder that could allow doctors to catch it before behavioral symptoms show up.

While autism is largely thought of as a cluster of developmental disorders, researchers at Imperial College London found dramatic differences in the amounts of metabolites released in the urine in autistic subjects when compared against healthy volunteers as well as their non-autistic siblings, including metabolites implicated in Parkinson's disease.

The findings, published Friday in the Journal of Proteome Research, back up earlier research suggesting autistic children demonstrate abnormalities in metabolism and even bear different colonies of microbes in their guts.

"What we were able to show was that autistic children were metabolically quite different from normal children," Jeremy Nicholson, a professor at Imperial College and head author of the paper, told DOTmed News. Nicholson helped found the field of "metabolomics," the study of chemicals produced by people and the bacteria that call them home.

Intriguingly, in the study, non-autistic siblings of autistic children were not "biochemically normal," Nicholson said, with metabolic profiles landing somewhere between full-blown autistic children and healthy controls.

"Non-autistic siblings actually have some of the same biomarker differences, but much less marked, so they were enough to make them statistically different from the control group, but distinguishable from autistic brothers and sisters," Nicholson said, making it "an interesting discovery in its own right."

In the study, the researchers matched urine samples of 39 autistic children aged 3 to 9 with 34 same-aged healthy volunteers and 28 non-autistic siblings. The urine samples for autistic children, their siblings and some of their controls came from University of South Australia. A second group of control samples came from the Swiss Tropical Institute. (Although diet is presumably quite different in Switzerland and Australia, urine make-up was statistically indistinguishable, the researchers said.)

The urine was analyzed with a device known as a nuclear medicine spectrometer, and the content of urine was compared to creatinine levels in the urine to control for liquid volume.

The findings were curious. Autistic children showed lower levels of the compounds hippurate and PAG, byproducts of digestion produced by gut microbes. PAG comes from the breakdown of proteins by gut flora known to help their hosts extract energy from food. Autistic children also have decreased levels of glutamate in their urine, also associated with energy metabolism, Nicholson said.

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