N-Acetylcysteine lowered irritability in children with autism as well as reducing the children's repetitive behaviors. Irritability affects 60 to 70 percent of children with autism. "We're not talking about mild things: This is throwing, kicking, hitting, the child needing to be restrained," said Antonio Hardan, MD, the primary author of the new study. "It can affect learning, vocational activities and the child's ability to participate in autism therapies."
Finding new medications to treat autism and its symptoms is a high priority. Irritability, mood swings and aggression are all considered associated features of autism and are treated with second-generation antipsychotics but those drugs cause significant side effects, including weight gain, involuntary motor movements and metabolic syndrome, which increases diabetes risk. By contrast, side effects of NAC are generally mild, with gastrointestinal problems such as constipation, nausea, diarrhea and decreased appetite being the most common.
Obviously, the findings must be confirmed in a larger trial before NAC can be recommended for children with autism. Hardan is an associate professor of psychiatry and behavioral sciences at Stanford and director of the Autism and Developmental Disabilities Clinic at Packard Children's. Stanford is filing a patent for the use of NAC in autism, and one of the study authors has a financial stake in a company that makes and sells the NAC used in the trial.
The state of drug treatments for autism's core features, including social deficits, language impairment and repetitive behaviors, also remains a major problem. "Today, in 2012, we have no effective medication to treat repetitive behavior such as hand flapping or any other core features of autism," Hardan said. NAC could be the first medication available to treat repetitive behavior in autism — if the findings hold up when scrutinized further.
The study tested children with autism ages 3 to 12. They were physically healthy and were not planning any changes in their established autism treatments during the trial. In a double-blind study design, children received NAC or a placebo for 12 weeks. The NAC used was a pharmaceutical-grade preparation donated by the neutraceutical manufacturer BioAdvantex Pharma. Subjects were evaluated before the trial began and every four weeks during the study using several standardized surveys that measure problem behaviors, social behaviors, autistic preoccupations and drug side effects.
During the 12-week trial, NAC treatment decreased irritability scores from 13.1 to 7.2 on the Aberrant Behavior Checklist, a widely used clinical scale for assessing irritability. The change is not as large as that seen in children taking antipsychotics. "But this is still a potentially valuable tool to have before jumping on these big guns," Hardan said.
In addition, according to two standardized measures of autism mannerisms and stereotypic behavior, children taking NAC showed a decrease in repetitive and stereotyped behaviors.
"One of the reasons I wanted to do this trial was that NAC is being used by community practitioners who focus on alternative, non-traditional therapies," Hardan said. "But there is no strong scientific evidence to support these interventions. Somebody needs to look at them."
Hardan cautioned that the NAC for sale as a dietary supplement at drugstores and grocery stores differs in some important respects from the individually packaged doses of pharmaceutical-grade NAC used in the study, and that the over-the-counter version may not produce the same results. "When you open the bottle from the drugstore and expose the pills to air and sunlight, it gets oxidized and becomes less effective," he said.
Although the study did not test how NAC works, the researchers speculated on two possible mechanisms of action. NAC increases the capacity of the body's main antioxidant network, which some previous studies have suggested is deficient in autism. In addition, other research has suggested that autism is related to an imbalance in excitatory and inhibitory neurotransmitters in the brain. NAC can modulate the glutamatergic family of excitatory neurotransmitters, which might be useful in autism.
The scientists are now applying for funding to conduct a large, multicenter trial in which they hope to replicate their findings. "This was a pilot study," Hardan said. "Final conclusions cannot be made before we do a larger trial."
The study is in the June 1st issue of Biological Psychiatry.