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.
Research suggests that the development of autism is rooted in very early brain development. However, in most cases, no one cause can be identified. Research has identified several genes that can cause autism in and of themselves. These account for about 15 percent of cases of autism spectrum disorders. Research has identified more than 100 genes or gene changes (mutations) that increase the risk that a child will develop autism.