An autism spectrum disorder (ASD) diagnosis has long been affiliated with an increased risk of celiac disease, but researchers have found that ASD may be linked to a positive blood test for gluten sensitivity, not celiac disease itself, according to a recent study.

Findings published online in JAMA Psychiatry reveal that there is no direct link between ASD and celiac disease. Researchers sought to compare celiac disease diagnosis among people with ASD to a group of people without the developmental disorder. They collected data from 28 Swedish biopsy registers on 26,995 individuals with celiac disease, 12,304 patients with inflammation of the small bowel, and 3,719 individuals with normal mucosa but positive celiac disease serologic test results. These participants were then compared with 213,208 age- and sex-matched individuals to examine the rate of diagnosis for people with ASD, as opposed to those without it.

The researchers found approximately 44 people per 100,000 were diagnosed with ASD before they were diagnosed with celiac disease compared to approximately 48 people per 100,000 who were diagnosed with ASD but not with celiac disease. While there was no direct link found between ASD and celiac disease, an autism diagnosis may increase the risk for a positive blood test for the condition.

"It could be a chance finding. Or it could be that patients with autism are more often tested for celiac disease. Or it could be a true biological cause, perhaps an increase in mucosal permeability. We speculate about this, but in our paper, we have no data on permeability, so hence, I cannot say,” said Jonas F. Ludvigsson, M.D., Ph.D., lead author of the study and professor of clinical epidemiology at the Karolinska Institutet in Sweden, to Medscape.

A positive blood test for gluten sensitivity does not warrant a celiac disease diagnosis. According to the Mayo Clinic, in order to be diagnosed with celiac disease, a patient must have a positive blood test and a negative biopsy. For individuals who do have a positive blood test for a gluten sensitivity with no evidence of damage done to the small intestine, they have latent celiac disease. This does not mean that they have been diagnosed with celiac disease but rather that they should remain cautious and use a “watchful waiting” approach. They should also do a repeat biopsy later on to see if they develop intestinal damage.

Dr. Ludvigsson assured ASD and celiac disease patients that this discovery is good news. "Celiac disease occurs in about 1% of the US population, and these patients were at no increased risk of autism," he said about the participants in the study. For ASD patients, a gluten-free diet may potentially have no effect on their autistic behaviors.

“A subset of individuals with ASD may have a condition that is triggered by gluten but is not celiac disease. This may help explain why gluten-free diets don't appear helpful for all cases of ASD but may be helpful for those who demonstrate these antibodies or gluten sensitivity. Studies examining this more closely would be useful,” Daniel Coury, M.D., professor of pediatrics and psychiatry at Ohio State University, told Medscape.

In the United States, at least one in 133 Americans suffers from celiac disease, while one in 110 Americans suffers from ASD, according to the Centers for Disease Control and Prevention. Currently, there is no cure for both medical conditions.