Environmental Exposure Measured in Deciduous Teeth As Potential Biomarkers of ASD Risk

Background: Gene/environment (G x E) interactions are now widely regarded as the most probable explanation for idiopathic autism.  However, in order for G x E interactions to be evaluated, valid biomarkers of exposure must be identified. Indeed, the largest roadblock to investigating adverse environmental exposures has been identifying valid biomarkers of exposures that occur during critical developmental periods. We have made significant progress this year with our discovery that semivolatile organic chemicals can be measured in shed deciduous teeth. We present further validation that chemicals measured in teeth can be used as biomarkers of early developmental exposure. 

Objectives: The purpose of our study was to determine if maternal retrospective reports about their children’s exposures to various chemicals would correspond to the chemical concentrations found in the child’s deciduous teeth. 

Methods: Seventy-one (71) deciduous teeth were chosen from our tooth repository consisting of 928 children’s deciduous teeth. These 71 teeth were to be analyzed for acetaminophen, DEET, pesticides, phthalates (plastics), and fatty acids. The selection of these teeth was determined by examination of survey responses provided by the mothers. We chose teeth based on both high and low self-reported exposures to determine if there would be a correspondence with chemicals measured in their children’s teeth. All children were recruited from the Interactive Autism Network (IAN) with diagnoses of autism. Electrospray ionization liquid chromatography tandem mass spectrometry (LC/MS/MS) in multiple reaction monitoring mode was used to determine the concentrations of targeted chemicals in the pulverized tooth samples. 

Results:  There was a 44% detection rate for acetaminophen, a 75% detection rate for insect repellant (DEET), a 13% detection rate for insecticide metabolites and from 40-100% detection rate across 4 phthalate metabolites. Among those self-reporting the highest cumulative use of acetaminophen, 53.5 percent (n = 23/43) had detectable amounts of acetaminophen in teeth compared to 28.6 percent (n = 8/28) detection in the lower exposure group (Fisher exact test = p <.051). DEET was regressed on self-reported repellant use yielding a .41 standardized beta with an R-square of .16 after adjustment for parental age and child gender (p<.002). Chi-Square analysis shows that 90.9 percent of those in the highest self-reported exposure category had detectable amounts of DEET in teeth compared to 63.3 percent detection in the lowest self-reported exposure group (fisher exact test = p <.01). There was a significant association between self-reported fume/chemical exposure and measured tooth phthalate metabolites during the time frames of pregnancy and after child birth (p<.05). There was no significant difference between self-reported pesticide exposure and pesticides measured in teeth.

Conclusions: Consistent with our prior report in the Journal of Exposure Science (Camann et al, 2013), we have demonstrated that specific semi-volatile organic chemicals can be detected in deciduous teeth. The current results indicate that mothers self-report of their child’s early exposure to acetaminophen, phthalates and DEET are consistent with measured amounts or detection in the child’s deciduous tooth. This provides some validation that teeth may be used as viable biomarkers of exposure during this developmental timeframe.