Association between hair lead levels and autism spectrum disorder in children: A systematic review and meta-analysis

Does Lead Have a Connection to Autism? A Systematic Review and Meta-Analysis

Environmental pollutants, particularly toxic trace metals with neurotoxic potential, have been related to the genesis of autism. One of these metals that stands out, in particular, is lead (Pb). We conducted an in-depth systematic review and meta-analysis of peer-reviewed studies on Pb levels in biological materials retrieved from autistic children (cases) and neurotypical children (controls) in this work. A systematic review was conducted after the careful selection of published studies according to established criteria to gain a broad insight into the higher or lower levels of Pb in the biological materials of cases and controls, and the findings were then strengthened by a meta-analysis. The meta-analysis included 17 studies (hair), 13 studies (whole blood), and 8 studies (urine). The overall number of controls/cases was 869/915 (hair), 670/755 (whole blood), and 344/373 (urine). This meta-analysis showed significantly higher Pb levels in all three types of biological material in cases than in controls, suggesting a higher body Pb burden in autistic children. Thus, environmental Pb exposure could be related to the genesis of autism. Since no level of Pb can be considered safe, the data from this study undoubtedly point to the importance of regularly monitoring Pb levels in autistic children.

Association Between Biological Lead Concentrations and Autism Spectrum Disorder (ASD) in Children: a Systematic Review and Meta-Analysis

Studies have been conducted in different countries of the world to illustrate a link between autism spectrum disorder (ASD) and lead (Pb) in different specimens such as hair, blood, and urine. Therefore, we carried out a systematic review and meta-analysis to determine the association between Pb concentration in biological samples (blood, urine, and hair) and ASD in children through case-control and cross-sectional studies. In this systematic review, PubMed, Web of Sciences, Scopus, and Google Scholar were searched for relevant studies from January 2000 to February 2022. A random-effects model was used to pool the results. The effect sizes were standardized mean differences (proxied by Hedges' g) followed by a 95% confidence interval. Pooling data under the random effect model from blood and hair studies showed a significant difference between the children in the ASD group and the control group in blood lead level (Hedges' g: 1.21, 95% CI: 0.33-2.09, P = 0.01) and hair level (Hedges' g: 2.20, 95% CI: 0.56-3.85, P = 0.01). For urine studies, pooling data under the random effect model from eight studies indicated no significant difference between the children in the ASD group and control group in urinary lead level (Hedges' g: - 0.34, 95% CI: - 1.14,0.45, P = 0.40). Moreover, the funnel plot and the results of the Egger test for the blood and urine samples showed no publication bias, while, for the hair samples, the funnel plot illustrated the existence of publication bias.

Exposure to lead on expression levels of brain immunoglobulins, inflammatory cytokines, and brain-derived neurotropic factor in fetal and postnatal mice with autism-like characteristics

Autism spectrum disorders (ASD) are neurodevelopmental disorders, and their incidence is increasing worldwide. Increased exposure to environmental metal lead (Pb) has been proposed as a risk factor associated with ASD. In the present study, BTBR T+ tf/J (BTBR) mice with ASD-like behavioral characteristics and control FVB mice were exposed gestationally and/or neonatally to Pb, and compared with highly social FVB mice to investigate neuroimmunological abnormalities. IgG1 and IgG2a levels in fetal brains from BTBR dams exposed to Pb (BTBR-Pb) were significantly higher than those of BTBR-controls (BTBR-C). However, this change did not occur in FVB mice exposed to Pb. The IgG1:IgG2a ratio was higher in both fetal and postnatal brains of BTBR mice compared to FVB animals regardless of Pb exposure. The IL-4:IFN-γ ratio was elevated in BTBR-Pb relative to BTBR-C mice, but this ratio was not markedly affected following Pb exposure in FVB animals. These findings suggest the potential for a Pb-driven predominant T_H2-like reactivity profile in brain microenvironment present in BTBR mice. Brain-derived neurotrophic factor was decreased in fetal and postnatal BTBR-Pb brains relative to BTBR-C brains but not in FVB-Pb relative to FVB-C mice. Taken together, data demonstrate that Pb exposure might contribute to developmental brain abnormalities associated with ASD, particularly in individuals with genetic susceptibility to ASD.

Correlation between lead exposure and cognitive function in 12-year-old children: a systematic review and meta-analysis

Lead exposure as a toxic material especially in children can be recognized as a harmful factor for cognitive function system. This meta-analysis was conducted to estimate the lead exposure effect on cognitive function among 6979 children less than 12 years. The 16 studies were divided into two clusters according to "duration of exposure" and "dose" using k-means partitioning clustering algorithm. Then, subgroup analysis has been performed based on the clustered studies. According to the results of the k-means clustering, dose and duration of exposure were significant factors between all considered variables. A stronger negative significant pooled correlation was observed in higher dose and duration cluster in comparison with another cluster including lower dose and duration (r = - 0.29, P-value < 0.001 vs. r = - 0.08, P-value < 0.001). Overall, a negative significant correlation was observed between lead exposure and cognitive function test score (r = - 0.22, P-value < 0.001). This study confirms the negative effect of lead on cognitive function in children, but needed further investigations to achieve the safe dose and duration of the lead exposure.

Exposure to lead increases the risk of meningioma and brain cancer: A meta-analysis

OBJECTIVE

To analyze the relationship between environmental lead exposure and various types of brain tumors.

METHODS

Search databases PubMed, Web of Science, Embase and Chinese National Knowledge Infrastructure (CNKI) as of July 1, 2019. Stata 15.0 software was used for analysis.

RESULTS

In the case control, lead exposure was associated with gliomas and meningiomas 0.82 (95 % CI: 0.69, 0.95) and 1.06 (95 % CI: 0.65, 1.46). In the cohort study, lead exposure was associated with brain cancer and meningiomas 1.07 (95 % CI: 0.95, 1.19) and 1.06 (95 % CI: 0.94, 1.17). The risk of childhood brain tumors associated with parental lead exposure was 1.17 (95 % CI: 0.99, 1.34).

CONCLUSIONS

Lead may be a risk factor for meningiomas and brain cancers. However, the glioma results suggest that lead may be a protective factor, which needs to be further studied.