Thursday, 22 November 2018

S Science

Environmental factors influencing the risk of autism

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Autism is a developmental disability with age of onset in childhood (under 3 years old), which is characterized by definite impairments in social interactions, abnormalities in speech, and stereotyped pattern of behaviors. Due to the progress of autism in recent decades, a wide range of studies have been done to identify the etiological factors of autism. It has been found that genetic and environmental factors are both involved in autism pathogenesis. Hence, in this review article, a set of environmental factors involved in the occurrence of autism has been collected, and finally, some practical recommendations for reduction of the risk of this devastating disease in children are represented. Keywords: Autism, environmental factors, etiological factors

 

INTRODUCTION

Autism described by Asperger (in 1938) and Kanner (in 1943)[1] is a severe neurodevelopmental disorder and belongs to autism spectrum disorders (ASDs), including autism, Asperger syndrome, Rett syndrome, unidentified pervasive developmental disorders, and childhood disintegrative disorder.[2,3] Autism is 4–5 times more common among boys than girls.[4,5,6] The most prominent clinical and phenotypic features of autism are extensive disabilities in social and behavioral communications, language impairment or inability to speak, and strong tendency toward stereotyped and repetitive patterns of behavior.[7,8] Regarding statistical reports, the prevalence of autism had increased from 4–5 cases per 10,000 children in 1980s to 30–60 cases in 1990s,[9] and through astonishing increase, there are about 8.0 per 1000 children aged 8 years in 2004 and 9.0 per 1000 in 2006 or 1 in every 110 children aged 8 years in 2006. In 2012, a combined ASD prevalence of 11.3 per 1000 children aged 8 years or 1 in 88 children was published by the Autism and Developmental Disabilities Monitoring Network.[7,10] With regard to its progressive increase over the last two decades,[11] and lack of effective treatment, and moreover, the difficulties imposed on the society and families of autistic children, the importance of investigation on causes of this disease and effort to prevent it become clear. There is growing body of evidence about genetic factors enrolment which is supporting autism etiology through genetic mutations (e.g., heritability and twins).[12,13] According to the important role of epigenetics in autism etiology, a lot of genes have been studied, and in some cases, opposite results obtained.[14,15] Studying identical twins and lack of complete concordance among them and excessive genetic studies with no conclusive results unveils the importance of environmental risk factors and their role in etiology of autism.[16,17] Hence, the interactions between susceptible genes and environmental factors have been proposed as the major mechanism of autism etiology.[18,19] Currently, epigenetic and its complex mechanisms are presented as the most momentous mediator in the environment and genome interactions.[20] Environmental factors can affect the quality and quantity of gene expression without changing the DNA sequence through epigenetic mechanisms, including DNA methylation, changes in histone proteins, and expression of noncoding RNAs. This way, they can be transferred to the next cellular generation or even the next organism generation.[20,21] As a result, exposure to harmful environmental factors can change the expression of developmental key genes in critical periods of embryo formation and increases the risk of genomic imprinting diseases such as autism.[22,23] None of the environmental factors is sufficient to yield autism, but rather a collection of them can be involved in the incidence of autism.[24] In this article, regarding mother and child exposure time to risk factors, they are divided into prenatal, natal, and postnatal risk factors.

 

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The world has to wake up to the toxic environment we have produced from the beginning of the industrial revolution. We have to clean up the planet's environment.

 
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