A link has been identified between elevated serotonin levels in children with autism and the following core symptoms of autism:

• Cognitive skill impairments
• Mood disorders
• Behavioral disorders
• Communication difficulties
• Verbal communication problems
• Speech ability
• Nonverbal communication difficulties
• Initiating and maintaining social interactions

An increase in these problems has been reported to be associated with elevated serotonin levels.

Additionally, research and quantitative analyses have been conducted as follows:
It has been determined that 40% of children diagnosed with autism who have good speech ability exhibit low serotonin levels.