Autism studies hampered by lack of reliable tests for bowel problems
Professor, Johns Hopkins University
Graduate student, Johns Hopkins University
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In his first description of autism in 1943, Leo Kanner described children with social problems, repetitive behaviors, and language difficulties. But another feature of his description would become a mainstay of autism: gastrointestinal distress1.2.
Since the publication of his report, dozens of studies have documented gastrointestinal problems, such as constipation, diarrhea and abdominal pain, in people with autism.
By some estimates, more than 70 percent of people with autism have gastrointestinal problems. But other studies have put the prevalence at 9%3. We believe these discrepancies are in part due to the way gastrointestinal issues are measured.4.5.
While there are good tools for assessing gastrointestinal problems in clinical practice, there are no reliable tools for use in epidemiological studies. For these studies, we need questionnaires that a participant or caregiver can complete outside of a doctor’s office.
Even the tools used by doctors have not been adapted for people with autism, who may have difficulty communicating. Some clinicians use parental reports to assess gastrointestinal symptoms in children. But parents may not always be aware that their child has cramps or abdominal discomfort, and instead may think that behavioral seizures rooted in pain are merely manifestations of autism.
While clinical or epidemiological tools can capture some gastrointestinal symptoms in people with autism, not all include questions about eating, eating behaviors, and other autism-related behaviors, such as than aggression and self-harm. These behaviors can signal bowel problems in a person who has difficulty communicating. In short, we just don’t know if these tools measure what we think is in people with autism.
The ability to accurately measure gastrointestinal symptoms in people with autism is extremely important for several reasons. It could reveal whether certain treatments cause them or make them worse. It could also tell us if they are linked to certain risk factors for autism, such as maternal immune activation, or if gut health itself is a risk factor for autism. And it could reveal whether treating symptoms can alleviate autism-related behaviors.
We looked at how researchers assess bowel problems in autism and how their results vary depending on the methods they use. We found that the severity and frequency of problems vary widely from study to study, and much of the variation is due to differences in the way the data is obtained.
To see how researchers test for these problems in autism, we searched until 1980 for any article on autism that included measures of symptoms. We found 144 studies. We focused on 84 studies that neither included nor excluded participants based on gastrointestinal symptoms or diet.
We calculated the median frequency of specific symptoms across studies and then performed statistical analyzes to determine whether the frequency of specific symptoms depends on the characteristics of the study participants or its methodology.
We found that the frequency of symptoms varied considerably from study to study. For example, the proportion of people with constipation ranges from 4 to 46 percent, and the rate of diarrhea ranges from 2 to 76 percent.6.
Studies also vary depending on who reported symptoms – whether that was a parent, teacher, doctor, or someone with autism. Interestingly, studies that do not specify who reported symptoms tend to report the most serious. Studies that use medical records or claims data report the highest frequency of reflux symptoms. And studies based in clinics or involving people at high risk for autism have the highest frequency of constipation.
The frequency of symptoms also depends on the age of people with autism: studies of people with an average age of 13 to 18 years report a higher frequency of abdominal pain and reflux than those involving younger children. This makes sense given that older children are probably better able to report more nuanced symptoms, such as pain and a feeling of reflux, than younger children.
Our results underscore the need for a standardized tool to assess gastrointestinal issues in autism. We believe that this tool should be a questionnaire that parents or caregivers fill out, especially when an individual is non-verbal, so that it can be implemented in large epidemiological studies.
A team of experts in gastroenterology, pain, diet, autism and questionnaire development should work together to develop the tool. People with autism and their parents should also be involved in this process.
It is important that the tool includes questions about eating, for example whether an individual avoids certain types of food based on texture, color, temperature or taste. He should also ask questions about mealtime behaviors, such as self-harm or aggression; and possible reactions to stomach pain, such as grimacing or applying pressure to the abdomen.
Some people may limit their diet due to gastrointestinal symptoms caused by certain foods. Alternatively, restrictive food preferences can lead to problems. Behaviors at and outside the table can be a response to bowel symptoms and pain.
Until this tool is developed, autism studies should clearly describe how gastrointestinal symptoms were measured. They should indicate which questionnaire was used, who reported symptoms and other important characteristics, such as the age and race of the participants.
Demographic characteristics can be linked to gastrointestinal symptoms, so this information can help researchers, clinicians, and families interpret study results. People with autism, their families, and the quality of research will all benefit from a standard and valid approach to measuring these symptoms in this population.
Danièle Fallin is pteacher and vsHair of the mental health service at Johns Hopkins University‘s Bloomberg School of Public Health and Ddirector of the Wendy Klag Center for Autism and Developmental Disabilities. Calliope Holingue graduated student in Fallinthe laboratory.