Published online Aug 7, 2014. doi: 10.3748/wjg.v20.i29.9942
Revised: May 22, 2014
Accepted: June 12, 2014
Published online: August 7, 2014
Autism spectrum disorders (ASD) comprise a group of neurodevelopmental abnormalities that begin in early childhood and are characterized by impairment of social communication and behavioral problems including restricted interests and repetitive behaviors. Several genes have been implicated in the pathogenesis of ASD, most of them are involved in neuronal synaptogenesis. A number of environmental factors and associated conditions such as gastrointestinal (GI) abnormalities and immune imbalance have been linked to the pathophysiology of ASD. According to the March 2012 report released by United States Centers for Disease Control and Prevention, the prevalence of ASD has sharply increased during the recent years and one out of 88 children suffers now from ASD symptoms. Although there is a strong genetic base for the disease, several associated factors could have a direct link to the pathogenesis of ASD or act as modifiers of the genes thus aggravating the initial problem. Many children suffering from ASD have GI problems such as abdominal pain, chronic diarrhea, constipation, vomiting, gastroesophageal reflux, and intestinal infections. A number of studies focusing on the intestinal mucosa, its permeability, abnormal gut development, leaky gut, and other GI problem raised many questions but studies were somehow inconclusive and an expert panel of American Academy of Pediatrics has strongly recommended further investigation in these areas. GI tract has a direct connection with the immune system and an imbalanced immune response is usually seen in ASD children. Maternal infection or autoimmune diseases have been suspected. Activation of the immune system during early development may have deleterious effect on various organs including the nervous system. In this review we revisited briefly the GI and immune system abnormalities and neuropeptide imbalance and their role in the pathophysiology of ASD and discussed some future research directions.
Core tip: According to the March 2012 report released by United States Centers for Disease Control and Prevention there was a 78% increase in the prevalence of autism spectrum disorders (ASD) during 2002-2008 in the United States. Although several genes causing ASD have been discovered, genetic cause of ASD is about 25% of cases. There was not a significant research focus on environmental factors and ASD-associated co-morbidities in the last two decades. We revisited the gastrointestinal (GI) involvement, GI infection, immune imbalance, maternal infection and immunity, and intestinal microflora in ASD. Some neuropeptides, neurotrophins, their effects, and side effects have also been discussed.