Our study is unique, since to our knowledge there are no published, long term population-based studies of the incidence of GI symptoms in children with autism compared to age- and gender-matched controls. We found no significant difference in the overall cumulative incidence of GI symptoms between cases and controls, although children with autism had a higher incidence of constipation and feeding issues/ food selectivity. We found few subjects with specific diagnoses of GI diseases, while the majority of both cases and controls had nonspecific GI symptoms.
Our findings are consistent with previous reports that have found that children with autism do not have an increased rate of either gastrointestinal disorders in general17, 18
or celiac disease in particular.19
In our study, the frequency of GI symptoms among both cases and controls was high (77.2% versus 72.2%, respectively). Prior studies have reported a 9% to 70% frequency of GI problems in children with autism.3, 4, 18
The highest previous estimates included lifetime prevalence of GI symptoms.4
Epidemiologic studies of the prevalence of GI symptoms in individuals with typical development have also shown high rates.20, 21
For example, a cross sectional prevalence study showed that 28% of normal 8 to 10 years aged school children were constipated.20
Further, a population-based survey of children 10 to 11 years of age showed that 27% of subjects reported some GI complaints during the last 2 years.18
The higher prevalence of gastrointestinal symptoms in our study reflects the cumulative incidence
during the period of follow-up to a median age of 18.2 in cases and 18.7 years in controls.
While we did not find an overall difference in the rate of GI symptoms between children with and without autism, we did find that children with autism were more likely to manifest feeding issues/food selectivity and constipation. The ritualistic tendencies, need for routine, and insistence on sameness that are characteristic of children with autism may lead these children to choose and demand stereotyped diets that may result in an inadequate intake of fiber, fluids, and other food constituents.17
Thus, behaviorally-related food selectivity may, in turn, lead to constipation.22
In a previous study, we reported that 52.4 % of the children with autism in this population were treated with stimulant medications to control symptoms of hyperactivity, impulsivity, and inattention.23
As appetite suppression is a known side effect of these medications, this may represent another factor that contributes to changes in eating patterns experienced by children with autism. Further, many children with autism are treated with risperidone, and this may result in increased appetite and weight gain.24, 25
Thus, it is possible that the difference in the incidence of both food selectivity and constipation that we found in children with autism compared to age and gender matched controls without autism is attributable to the behavioral features that define autism or to side effects of treatment with psychotropic medications, rather than to an underlying autism-specific organic gastrointestinal disease
Although we did not find an increased rate of GI diagnoses among individuals with autism on an epidemiologic basis, a number of gastrointestinal abnormalities have been previously reported in children with autism. For example, a chronic inflammatory process and increased intestinal permeability have been demonstrated by endoscopic and histological examination of the GI tract in some children with autism. 5–8, 26
However, these finding have not been replicated in other studies.27
Further, there have also been concerns raised about the potential role of the MMR (Measles, Mumps, Rubella) vaccine in the causation of autism.9
This theory hypothesizes that the MMR vaccine produces the enterocolitis that causes a “leaky gut” that leads to increased absorption of peptides with neurotoxic or neuroactive properties that produce the symptoms of autism 28
. This hypothesis was disproven in a recent study.29
In addition, introduction of the MMR vaccine has not been associated with an increase in complaints about gastrointestinal problems in children with autism.30
Further, a dramatically increased incidence of autism has been associated with the withdrawal of the MMR vaccine in Japan.31
We previously demonstrated that the introduction of mandatory MMR vaccination did not correlate with the apparent increase in the incidence of autism in Olmsted County, Minnesota.15
In the current study, we identified only one subject with autism and an inflammatory bowel disorder (Crohn's disease) in our cohort, as well as 1 with pancreatitis.
Autism is a chronic neurodevelopmental disability, and traditional medicine does not offer any cures. Thus, complementary and alternative treatments are widely provided to children with autism by parents who are searching for any biomedical intervention that they believe may help their children. Autistic behaviors are coincidentally first recognized by many parents at the same time that infants are weaned from breast milk or infant formulas and begun on whole milk and table foods, including table foods containing gluten. Combining this temporal relationship with belief in a GI-autism connection, where opioid-like peptides derived from casein and gluten are hypothesized to be absorbed through “leaky guts” to cause the symptoms of autism, many parents of children with autism are being advised to place their children on very restrictive gluten and casein free diets. However, evidence to support the safety and efficacy of gluten and casein free diets in the treatment of children with autism is lacking.32, 33
Urinary chromatographic profiles have shown no consistent patterns indicating excessive amounts of opioid-like compounds among individuals with autism.34–36
In addition, given the already increased food selectivity among children with autism, as confirmed in our study, further dietary restriction may place these children at risk for nutritional deficiencies.10, 26
In our cohort, we identified only 1 child with autism who had intestinal disaccharidase deficiency, while several control children had lactose intolerance or milk allergy.
Although hypothesized as another potential cause of a “leaky gut”, fungal overgrowth in the intestines has not been documented by endoscopy in children with autism.5
However, many parents of children with autism are encouraged to send samples of their children's urine to laboratories that claim to find urinary organic acids of fungal origin. Despite the lack of evidence to support their use or safety, many children with autism are then treated with systemic antifungal medications and/or other vitamin, mineral, or dietary supplements. While there is no evidence that these interventions improve autistic behavior, it is important to note that systemic antifungal medications are associated with liver toxicity, anemia, diarrhea, and exfoliative dermatitis.10
No subjects in our study, either cases or controls, had a history of intestinal fungal overgrowth.
Several potential limitations of our study should be noted. First our study was retrospective. Therefore, it is possible that we failed to detect all autism incidence cases or that some GI symptoms were undetected or incompletely documented in the medical records. However, given the increased medical scrutiny to which children with autism are subjected, it is unlikely that GI symptoms would be missed and not documented more frequently among autism cases than among controls. Furthermore, the completeness of the data and the availability of records for virtually all residents of Olmsted County minimize the possibility that cases of autism or information on gastrointestinal symptoms were missed. In the current study we did not compare the incidence of GI symptoms in children with cognitive impairment without autism to those with autism, but this will be interesting to explore in a future study. The population of Olmsted county was approximately 98% white between 1976 and 1997,37
which may limit the generalizability of these results to other populations. We also did not attempt to assess duration, severity, and recurrence of the GI symptoms in cases or controls in this study, as our main aim was to assess the prevalence of GI symptoms. This will be a goal of the next phase of this project