Manganese in autism spectrum disorder and attention deficit hyperactivity disorder: The state of the art

The objective of the present narrative review was to synthesize existing clinical and epidemiological findings linking manganese (Mn) exposure biomarkers to autism spectrum disorder (ASD) and attention deficit hyperactivity disorder (ADHD), and to discuss key pathophysiological mechanisms of neurodevelopmental disorders that may be affected by this metal. Existing epidemiological data demonstrated both direct and inverse association between Mn body burden and ASD, or lack of any relationship. In contrast, the majority of studies revealed significantly higher Mn levels in subjects with ADHD, as well as direct relationship between Mn body burden with hyperactivity and inattention scores in children, although several studies reported contradictory results. Existing laboratory studies demonstrated that impaired attention and hyperactivity in animals following Mn exposure was associated with dopaminergic dysfunction and neuroinflammation. Despite lack of direct evidence on Mn-induced neurobiological alterations in patients with ASD and ADHD, a plethora of studies demonstrated that neurotoxic effects of Mn overexposure may interfere with key mechanisms of pathogenesis inherent to these neurodevelopmental disorders. Specifically, Mn overload was shown to impair not only dopaminergic neurotransmission, but also affect metabolism of glutamine/glutamate, GABA, serotonin, noradrenaline, thus affecting neuronal signaling. In turn, neurotoxic effects of Mn may be associated with its ability to induce oxidative stress, apoptosis, and neuroinflammation, and/or impair neurogenesis. Nonetheless, additional detailed studies are required to evaluate the association between environmental Mn exposure and/or Mn body burden and neurodevelopmental disorders at a wide range of concentrations to estimate the potential dose-dependent effects, as well as environmental and genetic factors affecting this association.

Reference values of trace elements in blood and/or plasma in adults living in Belgium

OBJECTIVES

Trace elements (TEs) from natural and anthropogenic sources are ubiquitous. Essential or not, their relevance for human health and disease is constantly expanding. Biological monitoring is a widely integrated tool in risk assessment both in occupational and environmental settings. However, the determination of appropriate and accurate reference values in the (specific) population is a prerequisite for a correct interpretation of biomonitoring data. This study aimed at determining the reference distribution for TEs (Al, As, Sb, Be, Bi, Cd, Co, Cu, Mn, Hg, Mo, Ni, Pb, Se, Tl, Sn, V, Zn) in the blood and/or plasma of the adult population in Belgium.

METHODS

Blood and plasma samples were analyzed for 178 males and 202 females, recruited according to an a priori selection procedure, by inductively coupled plasma mass spectrometry (ICP-MS).

RESULTS

Reference values were established with high confidence for AsT, Cd, Cu, HgT, Mn, Mo, Pb, Sn, Se, Tl and Zn. Compared to previously published data in the Belgian population, a decreasing time trend is observed for Zn, Cd and Pb. Globally, the results also indicate that the current exposure levels to TEs in the Belgian population are similar to those from other recent national surveys.

CONCLUSIONS

These reference values and limits obtained through validated analytical and statistical methods will be useful for future occupational and/or environmental surveys. They will contribute to decision-making concerning both public health policies but also exposure assessments on an individual scale.

Assessment of gender and age effects on serum and hair trace element levels in children with autism spectrum disorder

The primary objective of the present study was to investigate the levels of essential trace elements in hair and serum in children with autism spectrum disorder (ASD) and investigate the age and gender effects. Children with ASD were characterized by significantly higher levels of copper (Cu) (+8%), iron (Fe) (+5%), and selenium (Se) (+13%) levels in hair and only 8% higher serum Cu levels. After stratification for gender, ASD boys were characterized by significantly increased hair Cu (+ 25%), Fe (+ 25%), and Se (+ 9%) levels, whereas in girls only Se content was elevated (+ 15%). Boys and girls suffering from ASD were characterized by significantly higher serum manganese (Mn) (+20%) and Cu (+18%) as compared to the control values, respectively. In the group of younger children (2-5 years), no significant group difference in hair trace element levels was detected, whereas serum Cu levels were significantly higher (+7%). In turn, the serum concentration of Se in ASD children was 11% lower than that in neurotypical children. In the group of older children with ASD (6-10 years), hair Fe and Se levels were 21% and 16% higher, whereas in serum only Cu levels were increased (+12%) as compared to the controls. Correlation analysis also revealed a different relationship between serum and hair trace element levels with respect to gender and age. Therefore, it is highly recommended to assess several bioindicative matrices for critical evaluation of trace element status in patients with ASD in order to develop adequate personalized nutritional correction.