Metabolic Genes and Blood Lead Concentrations in Jamaican Children with and without Autism Spectrum Disorders

Background: Autism Spectrum Disorders (ASD) are believed to involve both genetic and environmental factors in their etiology. Long-term exposure to lead has been shown to be associated with several glutathione-S-transferase (GST) family genes including GST mu 1 (GSTM1), GST pi 1 (GSTP1), and GST theta 1 (GSTT1) that play a major role in defense against oxidative stress which is linked to ASD.  

Objectives: To investigate the association between GST genes and ASD, either directly or through interaction with lead exposure, and to identify factors associated with blood lead concentrations (BLCs) among children in Jamaica.

Methods: We conducted a case-control study that enrolled children (age 2-8 years) from December 2009-March 2012. We used standard diagnostic tools to ascertain ASD in children from the Jamaican Autism Database at the University of the West Indies. For each confirmed ASD case, we identified an age- and sex- matched typically developing (TD) child as a control. We also administered a pre-tested questionnaire to assess demographic and socioeconomic information, parental education levels, medical history of children, and potential exposure to lead through parental occupation, home environment and food, with a particular focus on the types and amount of vegetables and seafood consumed by children. At the end of the interview, we collected 2 mL of whole blood from each child, which was analyzed for BLCs. Using a General Linear Model (GLM), based on data from 100 matched pairs, we assessed the association of BLCs with ASD status and sources of exposure to lead. We used multivariable GLM to control for potential confounders and to identify risk factors associated with BLCs. We used Conditional Logistic Regression (CLR) models to assess interaction between BLCs and GST genes in relation to ASD status.

Results: Nearly 93.0% of the ASD cases and 99.0% of TD controls were Afro-Caribbean. The mean age of the children in both groups was 69 months. In univariable GLM, we found a significant (P < 0.05) difference between geometric mean BLCs of ASD cases (2.25μg/dL) and TD controls (2.73μg/dL). However, when we controlled for potential confounders including parental education levels, place of child’s birth (Kingston vs. other areas), pica (habitually ate mud), consumption of shrimp and whole wheat bread, as well as using pots, pans, and dishes made of Teflon for cooking, there was no significant (P = 0.38) difference between adjusted geometric mean BLCs of ASD cases (2.49 µg/dL) and controls (2.79µg/dL). CLR models revealed a lack of significant interaction between BLCs and GST genes in relation to ASD status (all three P> 0.58). Additionally, in a separate multivariable GLM, we identified pica, consumption of freshwater fish, shellfish, and whole wheat bread as independent risk factors associated with BLCs in Jamaican children.

Conclusions: While our results do not support an association between BLCs and ASD, our data suggest that some Jamaican children may be exposed to lead through sources including consumption of shellfish, fresh water fish, and whole wheat bread. We recommend increasing awareness among parents regarding possible dietary sources of lead in Jamaica.