The talking point was supersized in 2000 when Medical Hypothesis, a fringe journal for junk scientists, published Autism: A Novel Form of Mercury Poisoning. When somebody writes Dandruff: A Novel form of Skin Cancer, it will also find a home in Medical Hypothesis. The 2000 paper was widely quoted by parents who needed something to blame. Mercury seemed so obvious - it is known to attack the nervous system, and it's present in thimerosal, and the symptoms of autism present right around the time that infants are immunized. So there ya go - case closed!
Yet a simple comparison of the clinical symptoms of mercury poisoning and the diagnostic criteria for autism shows they are quite distinct.
As Pediatrics tells us, the characteristic motor findings of mercury poisoning are ataxia (gross incoordination of muscle movements) and dysarthria (motor speech disorder).
The outcome of fetal methyl mercury poisoning in severe form also included spasticity. In contrast, in autism, the only common motor manifestations are repetitive behaviors (stereotypies) such as flapping, circling, or rocking. Persons with Asperger syndrome may be clumsy, and hypotonia has been noted in some infants with autism; the frequency of clumsiness and hypotonia in autism spectrum disorders is not established. No other motor findings are common in autism, and indeed the presence of ataxia or dysarthria in a child whose behavior has autistic features should lead to careful medical evaluation for an alternative or additional diagnosis.
Fetal exposure to mercury frequentlyt leads to microcephaly - a small head. But prenatal exposure to lead, alcohol, PCBs and other neurotoxins, for example, also tend to decrease head size. "In contrast", notes Pediatrics, "in autism increasing evidence indicates that head size and, as measured by volumetric magnetic resonance imaging, brain size tends to be larger than population norms."
I guess that's where the "novel" part comes in.
Cross posted at AutismNewsBeat.com