Autism (ASD) is one of the frequent neurodevelopmental disorders that children would occur. Many studies have shown that individuals with Autism are more common to experience significant gastrointestinal problems than other individuals. Symptoms include constipation, diarrhea, abdominal pain and gastric reflux. A recent study with 50 children with ASD, 50 children with other developmental disabilities and 50 healthy control children, it found that 70% of ASD children had presented with GI symptoms, compared with 42% of developmental disabilities children and 28% of developing children, it is believed that ASD children will have a distinctive microbial pattern in the stool. Attention-deficit/hyperactivity disorder (ADHD) is another neurodevelopmental and neurobehavioral disorder. A study found that ADHD individuals experience significantly higher rate of stomach pain and bowel problems than other control individuals. It is suggested that the microbiota in the stool of ADHD children might be different. Genetic study also found that if a child has a sibling with ADHD, the risk of developing ADHD is three to four times higher than that of children with siblings without ADHD.