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.
Almost everyone agrees that autism is caused by a combination of genetics and the environment. But while geneticists can comfortably rattle off lists of dozens of autism-linked genes, thereâs much less agreement about which environmental factors contribute to the disorderâand by how much.