Heavy Metals and Autism

Abstract

Autism is rapidly growing worldwide with massive impact on families, country and economy. Genetic and environmental causes are thought to be the main groups of aetiology of autism. Genetic mutations in multiple genes are identified, but they affect only less than 1/3 of cases. Environmental causes, specially trace elements deficiency and excess, leading to development of Autism Spectrum Disorder (ASD) through several mechanisms is discussed in this editorial, with a mini literature survey. However, satisfactory evidence for clear mechanism or aetiology of autism is still lacking. Thus delays the development of an effective treatment strategy for ASD. EditorialAutism Spectrum Disorder (ASD) is common and the numbers are outgrowing. Current prevalence is about 1% [1][2][3][4]. Changes in diagnostic criteria and improved awareness and reporting are amongst the reasons why the number is growing so rapidly, over the last three decades [2][3][4][5][6][7][8]. However, the numbers are growing so rapidly worldwide that it may show an increase in incidence beyond these confounders [3][4][5][6][7][8][9][10]. Diagnosis of ASD is difficult in the absence of a definite biomarker or anatomical site of defect and frequent changes in its diagnostic criteria. Subsequently the prevalence studies are also challenging [5].The aetiology of ASD is yet to discover, but there are genetic, epigenetic and environmental factors identified as possible causes. Numerous genetic variants have been identified by genetic sequencing of ASD patients and many said to involve glycosylation related proteins and enzymes [11].Many syndromes are known to associate with ASD such as, Rett syndrome, Fragile X, Tuberous sclerosis, Prader-Willi, Timothy syndrome, Phelan-McDermid syndrome, Harmartoma tumor syndrome [4]. On the other hand, the recent studies have shown a broad allelic overlap between autism and higher intelligence which opens a newer way of approach to search of genetic causes [12]. However genetic mutations that are identified account only for less than one third of ASD cases [13].The rapid increase in numbers during last few decades supports a major role in environmental factors over genetic causes alone [14,31]. The other possibility is that the environmental factors may be contributing to activate the genetic or epigenetic mechanisms of development of autism.The deficiency of some trace elements like zinc (Zn), manganese (Mn), molybdenum (Mo), Aluminium (Al) and selenium (Se) were found to be deficient in children with ASD [15][16][17]. Iron (Fe) deficiency and vitamin (eg: B9-folate) deficiency has also shown associations with ASD [18,19]. The excess of some elements like copper (Cu), lead (Pb), mercury (Hg) and cadmium (Cd) has also shown significant associations [15].Maternal micronutrient deficiency and toxin exposure can lead to defective foetal brain development. Prenatal exposure to pesticides, alcohol, cocaine, smoking and heavy metal can cause toxicity that leads to ASD [1]. Fish consumption, living close to gasoline stati...