Autism is a
neurodevelopmental disorder characterized by dysfunction in three primary behavioural domains: repetitive behaviours, social deficits, and language abnormalities. There is evidence that abnormalities exist in the
serotonin (5-HT) system in
autism spectrum patients. Furthermore,
5-HT is known to play a role in repetitive and social behaviours. This study examined the effect of
m-chlorophenylpiperazine (
m-CPP) on repetitive behaviours and
prolactin response in 11 adults with
autism or
Aspergers disorder and 8 age- and gender-matched healthy controls via randomized double-blind,
m-CPP and placebo challenges. The primary outcome measure was an instrument rating six repetitive behaviours: need to know, repeating, ordering, need to tell/ask, self-injury, and touching. Patients with
autism spectrum disorders showed a significant increase in repetitive behaviours at end-point following oral
m-CPP in comparison to placebo. Additionally subjects with
autism spectrum disorders showed a significantly increased
prolactin response to
m-CPP compared to normal controls, with neither group responding to placebo. This study provides further evidence for altered
5-HT sensitivity in individuals with
autism spectrum disorders, as well as a possible relationship between repetitive behaviours in
autism spectrum disorders and abnormalities in the
5-HT system.