A family history of mercury poisoning has emerged as a significant risk factor for developing autism, Melbourne researchers say.
A Swinburne University survey of 522 Australian survivors of pink disease - a form of mercury poisoning common in the early 20th century - found that one in 25 of their 398 grandchildren aged six to 12 had an autism spectrum disorder. The prevalence is six times higher than the one in 160 diagnosed in the general population.
The study, published this week in the Journal of Toxicology and Environmental Health, found the grandchildren did not have elevated rates of any other conditions such as epilepsy, Down syndrome, fragile X syndrome or attention deficit hyperactivity disorder.
The authors said although they did not validate the autism diagnoses provided by the survivors in the surveys their study added to mounting evidence of a link between genetics, mercury sensitivity and autism spectrum disorders.
They said the research also strongly suggested that autism was caused by a combination of genetic and environmental factors such as a family predisposition to mercury sensitivity and exposure to the metal in the environment.
''Since autism was first recognised as a disorder, scientists have been trying to identify its cause. There have been two warring camps: one that attributes autism to genetics and the other which claims it is caused by an environmental trigger,'' said Associate Professor David Austin, one of the authors of the paper. ''This study suggests that it may actually be a combination of the two. That is, genetic susceptibility to a trigger [mercury] and then exposure to that trigger. In this sense, it is like a peanut allergy. For most of us, peanuts are completely harmless but, for those who are allergic, there can be serious consequences if there is exposure.''
Professor Austin said his team was now examining the cellular and genetic characteristics of pink disease survivors and people with autism to try to understand the potential mechanisms.
He said people with a suspected family history of pink disease, especially young children and women who are pregnant and breastfeeding, should limit their exposure to mercury. ''This can be done by observing the recommendations of Food Standards Australia regarding seafood consumption, opting for non-amalgam dental fillings and requesting preservative-free vaccines from your doctor,'' he said.
Autism experts yesterday welcomed the study but said it should be repeated to test the findings, especially given the autism diagnoses were not independently confirmed after the survey.
Child and adolescent psychiatrist Bruce Tonge said although research had found some causes of autism, it was still largely unexplained. He said known causes included neurotoxins such as mercury, and infections during pregnancy including rubella and cytomegalovirus (CMV).