New lead on the cause of autism

Autism is on the rise, but what are the triggers? Image: Shutterstock

Psychoactive chemicals in drinking water cause genetic changes in fish similar to those associated with autism. 

Idiopathic autism is a behavioural disorder caused by genetic susceptibility coupled with some unknown environmental triggers. Scientists from Idaho State University School and the University of Wisconsin-Milwaukee have conducted a study that shows how low doses of unmetabolised psychoactive pharmaceuticals (UPPs) can cause gene expression changes in juvenile fish that mirror those associated with idiopathic autism.

The researchers exposed fathead minnows to a cocktail of psychoactive drugs — fluoxetine, venlafaxine and carbamazepine — and analysed the effects on the fish genome. “We think we’ve uncovered a potential source that might be a previously unrecognised trigger,” said Michael Thomas, lead author of the study published in PLoS ONE. “The expression of genes associated with neuron growth and synapse formation were changed, and these changes resulted in expression patterns similar to those found in individuals with a form of autism.”

Psychoactive pharmaceuticals are among the most frequently prescribed drugs. The use of antidepressants, such as SSRIs, by pregnant women has been shown to cause developmental issues in the child.

While the association between autism and psychoactive pharmaceuticals taken prenatally has been proven, the exposure to these drugs found in low doses in drinking water has commonly been overlooked. Furthermore, the authors explained that the maternal clinical usage of antidepressants is insufficient to account for recent increases in autism prevalence. In other words, it is very likely that an alternative source of exposure to these chemicals exists.

“The residual medications eventually end up in drinking water”¦ Which might be a human health concern especially for vulnerable populations (those with developing brains, like foetuses),” said Thomas.

The researchers tested the fish for genetic changes corresponding to various neurological conditions, such as Parkinson’s, bipolar disorder, Alzheimer’s and other forms of autism. They found that exposure to psychoactive medications only caused the genetic changes associated with idiopathic autism.  The results are significant and provide a new direction for research into the environmental triggers of idiopathic autism.

Gene expression patterns in humans and fish are quite similar — as these pathways are evolutionarily conserved — making the fish model a fairly accurate one. But the researchers want to look even further at the environmental “exposome” of autism and are now conducting cell culture work using human neuronal cells. They are also planning additional work with fish and mice models.

Source: PLoS ONE

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