Autism Spectrum Disorder (ASD)
While communication problems, social anomalies, and stereotypic behaviors are all part of autism spectrum disorder (ASD), autistic people can have other medical conditions. Because of their proven frequency and connection to the degree of core autism-related behavioral disorders, gastrointestinal issues are significant. According to Baird (2013), people with ASD have an increased chance of developing gastrointestinal problems, including celiac disease and celiac sprue. Gastrointestinal issues might affect ASD’s neuropathology and behavior and the emergence of autism-related end phenotypes, including immunologic dysfunction, hyperserotonemia, and metabolic disorders. A growing body of research suggests an association between gut-brain problems and ASDs, raising the possibility that these problems play some role in developing ASD symptoms. This paper focuses on the connection between gastroenterology and autism, which includes gastrointestinal problems and the gut-brain connection.
To diagnose ASD, doctors look for basic behavioral signs, including poor social interactions, difficulty speaking, and obsessive behavior or narrowed interests. Several neurological comorbidities accompany autism, such as intellectual disability, epilepsy, anxiety, and mood disorders (Mir et al., 2021). There are also non-neurological comorbidities like hyperserotonemia, immunologic dysregulation, and gastrointestinal abnormalities that are common in people with autism spectrum disorder (Chandler et al., 2013). It is commonly believed that ASD has several underlying etiology and development manifestations, which would explain the broad range of clinical differences seen among persons with the same ASD diagnosis.
Autism spectrum disorder has a variety of genetic and environmental risk factors, although only a small number of cases have a known etiology. There are no reproducible genetic diagnoses for ASD, and the condition is now identified through standardized behavioral testing rather than traditional clinical assessments. Treatment options for ASD’s symptoms are limited without a thorough understanding of the disorder’s molecular foundation. Most medications given to ASD patients are used to treat autism-related disorders like anxiety, impulsiveness, convulsions, and intense behaviors related to the disease. Given the diversity of ASD and the difficulty in discovering causes, therapies, or molecular indicators for the condition as a whole, a more detailed description of clinical ASD subtypes is needed.
Gastrointestinal Problems in Autism
Due to its established frequency and association with symptom intensity, stomach pain is one of the many medical problems associated with ASD. Many children with autism spectrum disorders have eating or nutritional issues, suggesting an early link between ASD and gastrointestinal abnormalities. Constipation, diarrhea, and stomach pain are the most commonly reported gastrointestinal problems among autistic people. Some autistic people have a higher incidence of gastroesophageal reflux disease (GERD), bloody diarrhea, throwing up, and gaseousness. They also have associated signs of gastrointestinal inflammation like nodular lymphoid hyperplasia, complement activation, and increased pro-inflammatory cytokines and intestinal pathologies like enterocolitis, gastritis, and esophagitis (Goldberg, 2004). Autistic children have higher levels of intestinal permeability, which may affect the intestinal barrier’s integrity and overall metabolome, allowing gastrointestinal metabolites or bacteria to be transferred and then activate their immune systems.
Food allergies, altered nutritional nutrient consumption, and metabolic abnormalities have all been related to autism spectrum disorder. Carbohydrate digestion is abnormal in autistic persons who also have gastrointestinal issues. The wide range of gastrointestinal diseases, nutritional problems, and abnormalities of the enteric immune system found in ASD patients suggest that GI malfunction may play a role in the emergence of the fundamental symptoms of autism.
Dysbiosis, or an altered microbiome composition, is a known occurrence in autistic individuals. When comparing people who are autistic with those who are not, researchers found that the former people had considerably higher amounts of Clostridium species (Goldberg, (2004). In autistic persons with anti-Sutterella serum antibodies, pyrosequencing of small bowel and caecum biopsies revealed a connection between Sutterella species and the presence of anti-Sutterella serum antibodies. Goldberg (2004) showed that the composition of the mucosal microbiome might influence complex behaviors such as anxiety, emotional or depressive behavior, and locomotion. However, the evidence is mixed; changes in the microbiota may have a role in the development or progression of autistic symptoms. Many bacterially modulated metabolites, including Clostridium-derived para-cresol, have been found in the urine of autistic children. These findings suggest that intestinal permeability and metabolic dysfunction may be linked to autism. Researchers hope that further studies with gnotobiotic mice will reveal if autism-related microbiome changes affect digestive function and behavioral phenotype.
Despite several studies on gastrointestinal dysfunction in autism spectrum disorders, it’s unclear if autistic people are more likely than controls to have gastrointestinal issues. According to Goldberg (2004), the prevalence of gastrointestinal problems ranges from 9 percent to 91 percent in people with an autism spectrum disorder. Hsiao (2014) has severe methodological problems, such as a lack of experimental controls, high variability in the sample population, a small sample size, bias in selection or referral, and a backward research design. The research of Hsiao (2014) also had a different method for identifying and describing gastrointestinal symptoms, which may have contributed to the vastly varied reported incidence of GI problems in autistic people compared to controls in the studies reviewed.
Researchers and clinicians working on ASD and GI found, despite these limitations, that “the preponderance” of data “was consistent with the possibility of a high incidence of gastrointestinal symptoms and disorders linked with ASD” (Hsiao, 2014). More than 14,000 ASD people were studied in a recent multicenter study (Hsiao, 2014). The results of the Hsiao study showed a higher frequency of intestinal disorders in ASD patients (0.83 percent vs. 0.54 percent) than in hospitalized controls (0.74 percent against 4.5%). As a result of the strong correlation between parents’ claims of GI difficulties in their autistic children. In Clinical diagnosis of GI abnormalities, researchers may be confident in their findings that autistic people have a higher incidence of GI disorders than the general population.
The Gut-Brain Connection in Autism
An increasing amount of information regarding the gut-brain axis, in which the GI tract and the brain link bidirectional to govern a range of functional activities, suggests that autism-associated GI issues may influence the development of core ASD symptoms. Many direct and indirect mechanisms may affect brain development and function as a result of gastrointestinal molecular alterations. Vibrations in the gastrointestinal microenvironment can alter vagus nerve stimulation afferents, which connect to the intestinal epithelium before traveling straight to the brain stem. They innervate the nucleus tract solitaries neurons. There are also several secondary projection sites for neurons in the nucleus tractus solitarius, including the central nucleus of the amygdala and the paraventricular nucleus of the hypothalamus (Hsiao, 2014). This system controls the transfer of mechano-sensory and chemical sensory stimuli from gastrointestinal tissues to the brain to govern GI processes, including motility, secretion, and satiation. Significantly, vagal nerve activity impacts various complicated operations, such as cognitive and emotional behavior, anxiety, and stress.
The immune system’s reaction to gastrointestinal symptoms can influence the brain and behavior and the body as a whole. Gastroenteritis, permeability, and altered microbiota makeup are all linked to functional gastrointestinal disorders. Autistic individuals’ gastrointestinal tracts show a variety of immunologic irregularities, including leukocyte infiltration, complement activation, lymphoid hyperplasia, and pro-inflammatory cytokine responses. People with autism and gastrointestinal difficulties have different immune responses and genomic profiles than autistics who don’t have these symptoms, which is in line with previous research. Additionally, autistic individuals have a variety of systemic immunological abnormalities that include a wide range of leukocyte responses to stimulation and a reduction in T cell abundance. The severity of a person’s behavioral scores on the autism spectrum is closely linked to alterations in peripheral immune profiles. There is also a link between patients with severe symptoms as evaluated by the Aberrant Behavior Checklist and aberrant plasma immunoglobulin profiles (Hsiao, 2014). When these findings are combined with the extensive research on the immunological effects on synaptic pruning, neuronal conduction, neural tube development, and glial specialization, among other neurological processes, alterations in the immune state may have an impact on autistic behavior.
It’s essential to consider the possibility that autism-related brain abnormalities lead to digestive tract problems. Mental illnesses such as sadness and anxiety are often linked to physical conditions like IBS. Indeed, severe depressive disorders are predicted to co-occur in 60% of people with functional gastrointestinal issues. Long-term psychosocial stress in animals has been linked to immunological and gastrointestinal (GI) disorders, including alterations in the microbiota in the gut, showing that the brain may impact gut function (Hsiao, 2014). Another study found that giving mice depleting drugs such as reserpine via injection into their ventricles made them more likely to develop an acute form of colitis (Hsiao, 2014). The relationship between chronic stress and depression, as well as stomach ulcers, may be the most well-known of these paradigms.
It is unclear if autism-related gastrointestinal issues arise from essential brain dysfunction or if some other unrelated factor causes them. Some GI abnormalities are linked to autistic behavioral core symptoms, which suggests that GI problems may influence the occurrence of ASD-related behaviors. However, this is not conclusive that autistic children with digestive issues display more significant irritation, anxiety, and social isolation, among other behavioral challenges. This suggests that the gut-brain connection plays a role in ASD.
Several studies also show conclusively that antibiotic treatment or a limited diet can successfully relieve autism-related behavioral problems. Casein and gluten-free diets, for example, have been found to improve behavior in autistic people (Hsiao, 2014). By inhibiting undigested casein and gluten peptides from reaching circulation, crossing the blood-brain barrier, and beginning neurotoxic events by binding to brain opioid receptors, it is anticipated that casein and gluten exclusion will damage brain function (Hsiao, 2014). If you exclude casein and gluten from your diet, it may help prevent intestinal lesions by reducing the immune system’s reaction. Furthermore, anecdotal support for the efficacy of casein- and gluten-free diet in curing fundamental autistic symptoms predominates over empirical data from rigorous scientific studies.
ASD is very varied, both in terms of the presence and severity of diagnostic behavioral features and a wide range of medical comorbidities. Given the challenges of identifying underlying causes, molecular indicators, and specific treatments for ASD, further research on subgroups of autistic people is required (Hsiao, 2014). Numerous findings suggest that gastrointestinal problems are common in autistic people and might have a role in the clinical presentation of ASD-related symptoms such as irrational behavior, immune system imbalance, and metabolic dysfunction. To determine the incidence of various gastrointestinal features in autism and to confirm present findings that certain GI problems are more common in specific subgroups of ASD persons, further randomized population-based studies are required.
An investigation into the effects of ASD genetic and environmental risk factors on the growth and differentiation of the GI tract will provide light on the molecular foundation for medical comorbidities seen in autistic persons. In addition, studying the effects of gastrointestinal issues on the brain and behavior in autistic animal models may give new approaches for establishing bio-molecular diagnostics and treatments for ASD. There is also a need for a better understanding of the role of intestinal microbiota in the immune system and metabolism, as well as in behavior, to help establish appropriate therapeutic guidelines for autism and encourage the development of new therapeutics that are more easily developed.
Mir, S. L., Sahito, A. M., & Ullah, I. (2021). Gastrointestinal symptoms and autism spectrum disorder: A Potential Link. Clinical and Experimental Gastroenterology, 14, 331. Web.
Chandler, S., Carcani-Rathwell, I., Charman, T., Pickles, A., Loucas, T., Meldrum, D.,… & Baird, G. (2013). Parent-reported gastrointestinal symptoms in children with autism spectrum disorders. Journal of Autism and Developmental Disorders, 43(12), 2737-2747. Web.
Goldberg, E. A. (2004). The link between gastroenterology and autism. Gastroenterology Nursing, 27(1), 16-19. Web.
Hsiao, E. Y. (2014). Gastrointestinal issues in autism spectrum disorder. Harvard Review of Psychiatry, 22(2), 104-111. Web.