Sunday, July 18, 2010
Censored on SafeMinds: New Scientific Evidence Links Autism to Vaccines and Mercury
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Posted at AoA on July 18, 2010 at 11:24am (EDT)
ReplyDeletePartI:
I'm curious why the names of the authors of the studies, let alone the article titles themselves, were not mentioned? How are readers supposed to even attempt evaluation of the study quality if they don't know which ones they are? For those interested, the studies are:
1st study: Hewitson L., Lopresti B., Stott C., Mason N.S., Tomko J. - Influence of pediatric vaccines on amygdala growth and opioid ligand binding in rhesus macaque infants: A pilot study
2nd study: DeSoto M.C., Hitlan R.T. - Sorting out the spinning of autism: heavy metals and the question of incidence
Some notes on the first study. First, no solid conclusions can be draw from it. It is a pilot study, in non-human animals, with a very small sample size.
The study used a total of 16 monkeys, 12 in the exposed group, 4 in the control group. More importantly, though, is that data for analysis (PET/MRI data) was only reported for 9 of the exposed group and 2 of the control group. An n of 2 is not enough to show anything with reliability or significance. This would be like having a group of individuals who enjoy eating kale, picking two at random and concluding that because both of them are short and overweight, that people who enjoy eating kale are generally short and overweight. It's faulty logic, to say the least. Further, there is no explanation about what happened to the 3 exposed and 2 control monkeys for which PET/MRI data was not reported.
There is also the issue that shrinking amygdala volume appears to be an anomaly. According to Payne, et al. in "Maturation of the hippocampal formation and amygdala in Macaca mulatta: A volumetric magnetic resonance imaging study", in typical macaques, the amygdala increases in volume as the monkey matures. In fact, the rate of growth appears to match quite closely to the rate of growth in the Hewitson study's exposed group. Granted, this study also has a relatively small sample size, though significantly more than the "normal" group in the Hewitson study. In light of the Payne study, some questions arise: why is there such a huge decrease in amygdala volume in the controls? Were the PET/MRI scans done incorrectly? Was there brain damage in the controls? Was the data manipulated to produce results in line with researcher expectations?
Finally, Hewitson, et al., explicitly mention that the increase in amygdala volume in the exposed group is not statistically significant. In other words, no reliable conclusion can be drawn from it.
Oh, and one other thing. Hewitson, et al., make no mention of autism. While the AoA community seems rather quick to extrapolate Hewitson, et al., to speak to the cause of autism, this is premature. Remember what happened when people touted Wakefield's retracted Lancet paper as evidence that MMR causes autism. His paper did not draw that conclusion, either, and people had to backpedal.
In short, Hewitson's paper cannot be used as a basis for the "vaccines cause autism" argument and is even a poor study for "vaccines cause brain damage" (remember that lack of statistical significance).
Part II:
ReplyDeleteThe DeSoto paper I have not read, yet, so I can't offer any comments on that, apart from the fact that it appears to be a literature review, rather than an actual study.
Calling for Congress to pass legislation banning mercury in vaccines is premature. There just isn't a strong scientific basis for such a ban, and the two studies cited by SafeMinds are no different. Although I agree that we should constantly work to find better, safer alternatives and to reduce the amount of unnecessary exposure to mercury in whatever form (and the form and use of the mercury are important), measures that have a bearing on science should be based on sound, relevant science.
I would like to end, though, by addressing a comment by Jenny Allan. Regarding thalidomide, remember that it was an FDA investigator that prevented thalidomide from being approved for marketing in the U.S. for the treatment of nausea in pregnant women. This prevented the level of injuries seen in Europe.
Oh, I almost forgot to mention another glaring hole in the Hewitson study: no conflict of interest statement, such as the fact that Hewitson's child is a claimant in the Autism Omnibus proceedings.