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.
Researchers are examining a number of specific genes that could contribute to the disorder. It's likely that autism occurs when a small number of genes interact in a specific way, possibly linked to some external event or factor. The genetic link means a predisposition to autism may be inherited and can run in families.