Thousands of microvilli form a structure called the brush border that is found on the apical surface of some epithelial cells, such as the small intestines. (Microvilli should not be confused with intestinal villi, which are made of many cells.
Autism spectrum disorder has no single known cause. Given the complexity of the disorder, and the fact that symptoms and severity vary, there are probably many causes. Both genetics and environment may play a role. 1  Genetic problems. 2  Several different genes appear to be involved in autism spectrum disorder.
A revision to autism spectrum disorder (ASD) was proposed in the Diagnostic and Statistical Manual of Mental Disorders version 5 (DSM-5), released May 2013. The new diagnosis encompasses previous diagnoses of autistic disorder, Asperger's disorder, childhood disintegrative disorder, and PDD-NOS.hile a specific cause or specific causes of autism spectrum disorders has yet to be found, many risk factors have been identified in the research literature that may contribute to the development of an ASD.