Autism spectrum disorders (ASD) are complex neurodevelopmental disorders characterized, in varying degrees, by impairments in social interaction, communication, and restricted and repetitive behaviors. For every 10,000 children, approximately 20 are affected by ASDs, which are usually identified before 2 years of age through a hallmark of symptoms. Generally, these symptoms are divided into two categories: core and secondary. Core symptoms include a reduction in language skills and reciprocal deficits in social interaction whereas secondary symptoms include complications such as self-injury, hyperactivity, aggression, and co-occurring psychiatric disorders such as anxiety and major depression. The presentation of these impairments is variable in range and severity and may change depending on the affected individual’s developmental progress.
The umbrella term of “ASDs”, describes a number of disorders including Autistic disorder, Asperger’s syndrome, Pervasive developmental disorder-not otherwise specified (PDD-NOS), and childhood disintegrative disorder . Diagnosis for ASDs occurs on a spectrum where Asperger’ syndrome is on the milder end since afflicted children and adults primarily have difficulty with social interaction. These people may be very intelligent and may immerse themselves into their interests and talk about them non-stop. Children whose autism is more severe than Asperger’s but not as severe as autistic disorder are grouped under the PDD-NOS title . In fact, autistic disorder can be distinguished from the two former ASDs by the delay in language development and the severity of behavioral and intellectual impairments. However, the most rare and most severe ASD, childhood disintegrative disorder, is characterized by the rapid loss of mental, social, and language skills between the ages of two and four. These children typically also develop seizures.
Although the exact cause of autism and other ASDs remains unknown, it is believed that development of ASDs is a result of both genetics and the environment. Family studies and twin studies have demonstrated the role genetics plays in the development of ASDs. The recurrence rate in siblings of an autistic child is 2-8 % greater than that of the general population . Other studies suggest that alongside the complexity of the disorder, the mode of disorder inheritance itself is very complex, with linkage studies suggesting a relationship between genetic loci on multiple chromosomes (7, and X). In addition to genetic factors increasing the risk for ASDs, there is accumulating evidence that environmental factors contribute to the pathophysiology of ASDs. Environmental exposure to a number of toxins can alter brain development and affect processes such as axon myelination, the aberrant breakdown of which causes multiple sclerosis, cell differentiation, and the formation of connections between neurons. A number of epidemiological studies have shown that prenatal infections with rubella and cytomegalovirus, accounts for few cases of autism, and some studies, though it remains a matter of debate, have suggested the exposure to heavy metals plays a role in developing ASDs . Also, maternal lifestyle and diet, more specifically their deficiency in essential nutrients and fatty acids, is associated with neurodevelopmental consequences associated with an increased risk for ASDs .
The role of environmental factors in the development of ASD is an area of active research. Although several studies have demonstrated the association between the environment and ASD, it is important to point out that no single environmental factor is sufficient to significantly influence the predisposition to ASD. Rather, it is the combination of several environmental and genetic factors that are likely to have a significant impact on ASD development.
Despite the variability in the degree of impairment, individuals afflicted with these disorders and their loved ones are subject to social, educational, and occupational challenges. Currently, very few treatments are available, most of which are behavioral and have limited impact on core behavioral symptomology. Continued research in this field will focus on developing the underlying causes of these disorders with the aim of developing new tools for the early detection and diagnosis of children with a high risk for ASD.
By Azizia Wahedi
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