Geiers Target Dental Amalgam

The father-son duo, along with frequent coauthor Janet Kern, were able to publish yet another study implicating at least some kind of link between mercury (this time from maternal dental fillings) and the severity of childhood autism. But the authors missed on what would generally be construed as the primary endpoint of their study. The negative finding is buried in the latest issue of Acta Neurobiologiae Experimentalis (Warsaw), a journal with an impact factor in the 25th percentile.*

For anyone familiar with the Geiers' previous publications, there is little shock value here. Evidently the authors remain incapable of disinterest. The introduction of the article preferentially cites highly questionable data linking mercury in dental amalgam with various bodily dysfunctions generally and autism spectrum disorder (ASD) specifically. And in consistent form, the Geiers cite their own previously published data to bolster their preformed ideas.**

The study methods are vague and fraught with potential bias: They write, "The present study looked at 100 qualifying participants who were prospectively recruited from patients presenting for outpatient genetic consultations at the Genetic Centers of America." Mark Geier is president of the "Centers," which are evidently located in the basement of his residence in Silver Spring, MD. The study is also described as blinded, although it's not clear who is blinded to what. The subjects, born either from 1990 to 1999 or between 1990 and 1999, were "previously diagnosed" with autism or pervasive development delay (PDD) by a "trained professional." As far as the reader knows, this term could refer to an autism specialist, a general pediatrician, a chiropractor, a naturopath, or a plumber. The study protocol itself is described as being approved by the Institutional Review Board (IRB) of the Institute of Chronic Illnesses, another brainchild of Mark Geier. The makeup and objectivity of this IRB has been called into serious question.

The primary finding of the study was that there was no statistically significant difference between the mean number of maternal dental fillings during pregnancy and the severity of autism. After adjusting for age, sex, race, and geographic residence, mothers of children with autism (defined as "severe") had 4.6 fillings, and mothers of children with ASD (defined as "mild") had 3.1 fillings (P = .0946). (Of course, the arbitrary distinction of severe and mild autism on the basis of the prestudy diagnoses, one of which includes the term "spectrum," is highly problematic.)

Undaunted, Geier et al attempted to define a threshold number of maternal dental fillings that significantly elevated the risk of "severe" autism. After performing a "logistic regression analysis," they concluded that the odds of "severe" (vs "mild") autism more than tripled if the number of maternal dental fillings during pregnancy exceeded 5; however, the risk was only statistically significant with 8 or more fillings. The "threshold" finding is the only conclusion cited in the article's abstract.

The most profound limitation (and there are several...arguably many) of this study is the lack of any data from a control population—namely the mean number of dental fillings in mothers whose children do not have autism.

* For comparison purposes, the NEJM has an impact factor of greater than 99%.

** In the opening paragraph, Geier et al write, "As of mid-2008, the US Food and Drug Administration (FDA) has declined to classify the medical-device safety of amalgams used in dentistry [emphasis added]." Given the article's recent publication date, this statement suggests that Geier et al had been shopping this article around for some time. The FDA issued its final regulation on dental amalgam in July. The mercury component of dental amalgam was reclassified from Class I (low risk) to Class II (moderate risk).