Case Report: Allergic reaction following fecal microbiota transplantation in children with autism spectrum disorder: a report of two cases (Jun 2026) FMT

[Michael Harrop]

https://www.frontiersin.org/journals/pediatrics/articles/10.3389/fped.2026.1847568/full

Abstract​

Background:

Fecal microbiota transplantation (FMT) is increasingly used in children with autism spectrum disorder (ASD) and is generally considered to have an acceptable safety profile. However, the risk and mechanisms of severe adverse events in the high-risk subgroup of children with ASD complicated by multiple food intolerances (FI) have not been reported, and clinical strategies for risk prevention and management remain lacking.

Case report:

This article reports two cases of children with ASD and multiple FIs who developed anaphylactic shock following FMT, representing the first such report in the pediatric field. Case 1 presented with early-stage shock, which was considered to be associated with IgG-mediated type III hypersensitivity. Case 2 developed classic anaphylactic shock with a biphasic course characterized by relapse after initial resolution, raising the possibility of biphasic anaphylaxis. Both children improved after standardized anti-allergy and anti-shock treatment, and one child successfully completed subsequent FMT using a low-dose regimen.

Conclusion:

FMT carries a risk of anaphylactic shock in children with ASD and multiple FIs, who have underlying susceptibility due to impaired intestinal barrier function and immune dysregulation. Refined risk stratification, close monitoring throughout the procedure, individualized transplantation protocols, and standardized emergency procedures can effectively enhance the safety and feasibility of FMT in this high-risk subgroup.

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Donor information: The fecal microbiota suspension was provided by Shenzhen Qiyuan Future Biotechnology Co., Ltd., sourced from a 10-year-old healthy male (batch number GZ001). Five days prior to stool donation, the donor underwent dietary restrictions to avoid foods to which the recipient was allergic or intolerant. The donor tested negative for common allergens. The donor's gut microbiota composition was assessed using 16S rRNA high-throughput sequencing. Microbiota diversity was similar to that of healthy children of the same age, with no significant dysbiosis and a relatively stable community structure. At the phylum level, Bacteroidetes was the dominant phylum, and no pathogenic bacteria were detected. The donor met the general screening safety standards for pediatric fecal microbiota transplantation.

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The proposed mechanism is as follows: components of the donor microbiota or the transplant suspension may have entered the circulation through the compromised intestinal barrier and formed IgG–antigen complexes.

Further analysis suggests that the donor suspension may have contained histamine-producing bacteria (e.g., Escherichia coli, Proteus species), leading to increased histamine production.

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[SFBayFMT5]

That's interesting... both because donor avoidance of allergens didn't prevent the problem, and also because this was a classic anaphylactic reaction. Many of us on the autism spectrum have food sensitivities and/or allergies, but it was my understanding that classic allergic reactions like asthma, hives, etc. are rare in this population, with GI complaints and/or mood swings and other neuropsychiatric effects (that allergists often fail to correctly identify as food reactions, even when later elimination diets show that they were) being much more common.