20 April 2013. Autism and related disorders appear to increase in frequency in many countries. Although the extent of this increase is a matter of controversy, the causation of the disease – and ways to prevent it – are poorly known. Chemical brain drain is a highly likely contributor, and a new study from Finland adds support to this notion.
The researchers analyzed maternal serum collected during pregnancy and compared the chemical concentrations between 75 autism cases and 75 healthy control children who were otherwise comparable to the cases. The new report presents results on PCBs and the pesticides DDT and hexachlorobenzene. Due to the relatively small number of subjects, the results were not statistically significant. However, the sum of PCBs and the DDT breakdown product DDE showed clear tendencies of higher exposures among the autism cases (odds ratios of 1.9 and 1.8 for PCBs and DDE, respectively). Mothers whose children were later diagnosed with autism were about twice as likely as control mothers to show serum PCB and DDE concentrations among the highest 10%.
This new finding, although preliminary, is important. First, the researchers demonstrated that a case-control design is feasible and can be successfully carried out using stored maternal serum samples collected during pregnancy. Over the years, the Finns have stored about 1 million serum samples in large freezers, so we should expect more evidence to emerge from this corner of the world. Similar, though smaller biobanks exist in many other countries. The new study provides inspiration to replicate and extend these findings.
Second, most evidence on environmental chemicals so far has focused on exposures of autistic children only after the diagnosis. However, the causative exposure must have happened much earlier, most likely during fetal development. So the results are of little use, even though some have suggested links to mercury or other known brain drainers. Other research has linked autism frequencies to various air pollutants. But air pollution is a complex mixture, and it varies from time to time. In general, because the exposure assessment is imprecise, these studies likely underestimate the real contribution of the exposures to autism causation.
Thirdly, the results should also be considered in light of other evidence on chemicals: Certain drugs, such as thalidomide, misoprostol, and valproic acid, if used during pregnancy, can lead to an increased risk of autism in the child. Maternal alcohol use and German measles infection during pregnancy are also known contributors to autism risks. (Childhood vaccination has been suspected as a risk factor, but large studies do not support this notion.) So exposure to toxic chemicals during early brain development is a highly plausible risk factor for autism.
Still, autism clearly has a heritable component, and for this reason interactions between genes and environmental chemicals may be of critical importance in the disease development. In order to decipher such interactions, very large studies are needed.
The bottomline is, autism should be considered an outcome of chemical brain drain.