Autism is a pervasive neurodevelopmental variation that occurs in approximately 2% of the human population. Compared to neurotypical individuals, autistic individuals tend to have a sensory experience that is more intense and unfiltered. Due to differences in social behavior and body language, autism is almost always a disability.
Common signs of autism are usually displayed before the age of 3 and last throughout the life of the individual. Below is a list of those attributes:
- situational or pervasive mutism, typically affecting oral speech only and not writing
- difficulty intuitively learning and recognizing the body language and other non-verbal communication of non-autistic people
- preference for routine and sameness
- repetitive body movement (stimming) such as flapping one's hands as an expression of emotion or for self-regulation
- sensitivity to sensory input such as bright lights and loud sounds; may result in avoidance or seeking of said input
- preference for logic and literal use of language
Though the cause of autism has not been pinpointed to a specific source, experts concur that like other neurodevelopmental conditions, autism can be attributed to both genetic and environmental factors.
No gene has been implicated as a definitive cause of autism. However, twin studies have demonstrated a strong hereditary basis, and many researchers have found specific genes associated with an increased chance of autism.
The environment also can result in de novo mutations, mutations that occur for the first time in a family member as a result of a mutation in either a sperm or egg cell. A correlation between paternally inherited DNA and paternal age shows that autistic boys were six times more likely than neurotypical boys to have a father in his 40s. Maternal infection has also been widely accepted as a risk factor.
Other implicated environmental risk factors allegedly alter the development of a young child's brain, rather than regulate the expression of genes. Vaccines and pesticides are two such factors. While the autism-vaccine hypothesis has been discredited by the scientific community, several studies in the U.S. have made an effective case for an autism-pesticide link, although a European meta-analysis of four large studies found no such association.
"Autism - Topic Overview." WebMD. Healthwise, 10 Apr. 2010. Web. 6 Dec. 2012. <http://www.webmd.com/brain/autism/autism-topic-overview>.
Insel, Thomas. "The New Genetics of Autism – Why Environment Matters." National Institute of Mental Health. N.p., 4 Apr. 2012. Web. 6 Dec. 2012. <http://www.nimh.nih.gov/about/director/2012/the-new-genetics-of-autism-why-environment-matters.shtml>.
DeWeerdt, Sarah. "Why don't we know what environmental factors cause autism." Spectrum. 4 Nov. 2015. <https://spectrumnews.org/features/why-dont-we-know-what-environmental-factors-cause-autism/>