Methylmercury and Measures of Attention Deficits in the ELEMENT Cohort.

Abstract

Attention-deficit/hyperactivity disorder (ADHD) is one of the most common psychiatric disorders in school-age children and is the cause of multiple burdens related to healthcare costs, academic performance, and later employment. As such, its etiology represents a major public health concern. While genetics play a large role in the etiology of ADHD, multiple environmental exposures may contribute to risk. Here, we investigate the role of one toxicant, methylmercury (MeHg), measured in hair and blood, and its possible interactions with both other toxicants (lead, Pb) and a series of candidate genes. Additionally, we examined possible associations of MeHg exposure with the acoustic startle reflex (ASR) and the sensorimotor gating process, prepulse inhibition (PPI), in which deficits have been observed in individuals with attention deficits. Participants were recruited from the Early Life Exposure in Mexico to Environmental Toxicants (ELEMENT) study, a longitudinal birth cohort that began in the 1990s. ADHD symptoms were screened using the Conners’ Continuous Performance Test II (CPTII) and the Conners’ Rating Scales-Revised (CRS-R). We found no significant associations between prenatal and postnatal MeHg exposures and ADHD screening scores. No interaction was seen for concurrent exposures to MeHg and Pb. For prenatal exposure, generally, interactions between the two metals corresponded to increasing attention deficits scores in trimester 1, while interactions between the two corresponded to decreasing attention deficits scores in trimester 2, and no pattern was seen in trimester 3. Additionally, we found that associations between hair Hg concentration and attention measures differed by dopamine receptor D4 (DRD4) and catechol-O-methyltransferase (COMT) genotype. ASR without a prepulse was non-linearly associated with MeHg exposure. For ASR response magnitudes with prepulses, higher MeHg generally corresponded to higher ASR magnitudes, especially in the right tail of their respective distributions. No significant associations were seen between MeHg and PPI. This research adds to our understanding of how environmental influences like MeHg can play a role in the development of attention deficits in children and adolescents.