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.
Brain development and autism spectrum disorder. In children with autism spectrum disorder (ASD), the brain develops differently from typically developing children: 1  The brain tends to grow too fast during early childhood, especially during the first three years of life.enetic factors seem to play a major part in autism spectrum disorder (ASD). For example, some families have multiple children diagnosed with ASD. Many of these families have higher rates of language and anxiety disorders.