Exploration in the aetiology of Autism Spectrum Disorder

A common question associated with Autism Spectrum Disorder (ASD), is what causes it? The precise cause is unknown, although there is significant research into the aetiology of the disorder that provides some insight.

ASD is believed to be caused by multiple influences such as environmental, biological and genetic factors. The influences of these factors may explain the spectrum of behaviour observed in people with ASD. ASD may be associated with various conditions affecting brain development such as maternal rubella (including other viral diseases of the central nervous system) or post-encephalitic neuroinflammation but this link remains unclear. Some research has hinted at the possibility of ASD being caused by fragile X syndrome, encephalitis and untreated phenylketonuria.

Fragile X syndrome is a genetic condition which causes developmental problems, including ASD. It affects males more severely than females, and affected persons characteristically have delayed speech and language development. One third of females affected are intellectually disabled with most males having moderate intellectual disability. About one-third of people with fragile X syndrome have features of ASD. Fragile X syndrome is the most prevalent known single gene cause of ASD.

Autoimmune encephalitis is where the immune system attacks the brain- impairing its function. Research has suggested that children with ASD have a brain pathology indicating ongoing neuroinflammation or encephalitis. It is estimated that around 69% of children with ASD have neuroinflammation- however children who are diagnosed with ASD are not typically tested for encephalitis. This means that if a child has developed ASD as a result of encephalitis, they could receive treatment that reduces the deficits of ASD.

Phenylketonuria is a fault in the metabolism that leads to the decrease in metabolic activity involving the amino acid phenylalanine. It is an inherited disorder and is due to the mutation in the PAH gene which subsequently influences the levels of the enzyme phenylalaline hydroxylase- significantly lowering them. Left untreated, it can lead to intellectual disability and possibly autism.

Maternal rubella is associated with ASD, it was found that children with ASD had an “altered immune response to rubella vaccination” (5), this suggested that they had already been affected by rubella. With Chess (1971) finding that children with congenital rubella had an increased incidence of ASD. It was suggested from this that congenital rubella of the central nervous system could produce the complex and severe social deficits of ASD.

This is only small insight into the possible aetiology of autism spectrum disorder, however current research is providing more evidence for the possible causes of ASD.

Bibliography:
1. https://fragilex.org/learn/#1496329540057-84f46e65-cbb0 [Accessed 03/05/2018]
2. https://ghr.nlm.nih.gov/condition/fragile-x-syndrome [Accessed 03/05/2018]
3. Kern, Janet K., et al. “Relevance of Neuroinflammation and Encephalitis in Autism.” Frontiers in Cellular Neuroscience, vol. 9, 2016, doi:10.3389/fncel.2015.00519.
4. https://en.wikipedia.org/wiki/Phenylketonuria
5. http://www.jneurovirol.com/o_pdf/11%281%29/001-010.pdf

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