A new study, led by researchers at Stanford University and the Cleveland Clinic, has identified N-acetylcysteine (NAC) as having the potential to reduce irritability in individuals with autism. NAC, which has already been approved by the US Food and Drug Administration for the treatment of Tylenol overdoses, proved effective at significantly decreasing irritability in autistic children during a pilot trial.
NAC helps to maintain and restore glutathione (GSH), which is a tripeptide that plays an important role in the antioxidant defence system. NAC treatment also provides cysteine which stimulates a cystine-glutamate antiporter; a process which helps to decrease glutamatergic neurotransmission. The effects of NAC treatment are twofold. By raising the level of glutathione – a projective antioxidant metabolite – it can protect brain cells. It can also lessen the excitability of the glutamate system by stimulating inhibitory receptors.
Although scientists do not understand the exact causes of autism, it is believed that the disorder is influenced by a variety of factors. Two of these proposed factors are connected with NAC. One theory states that autism could be caused by an imbalance between oxidants and antioxidants, whilst another proposes that those with autism may possess dysfunctional glutamate systems.
In the pilot trial – the results of which will be published in the journal Biological Psychiatry
– children with autism were randomised to receive either NAC or a placebo over the course of 12 weeks. Their symptoms were evaluated four times during this period. The researchers discovered that irritability was significantly reduced in the participants who received NAC. Moreover, the treatment precipitated few side effects.
"Data from this preliminary trial suggest that NAC has the potential to be helpful in targeting irritability in children with autism," said Dr Antonio Hardan, Associate Professor at Stanford School of Medicine and lead author of the study. "It is also unclear if NAC improves other symptom domains in autism.
"[Large] randomised controlled trials are needed to attempt to replicate the findings from this pilot trial and to determine whether or not NAC is effective in targeting other symptoms observed in autism such as repetitive and restricted interests," he added.
Irritability amongst those with autism can adversely affect individuals’ abilities to function, both domestically and educationally. The symptom can manifest itself as aggression and can even lead to self-injurious behaviour. Whilst the researchers do not yet fully understand the ramifications of their findings, it is hoped that this study could enhance our ability to combat irritability in those with this disorder.
"At this point it is too early to tell how NAC reduced irritability in autism, but this finding will be an important addition to the field if it can be replicated," explained Dr John Krystal, Editor of Biological Psychiatry