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.
Itâs important to know that there are three quite different types of autism spectrum disorders: autistic disorder or what is called classic autism, Asperger syndrome and pervasive developmental disorder â not otherwise specified (atypical autism). The most common form of autism spectrum disorder is classic autism.