Association between allergic diseases and autism spectrum disorder: protocol for a systematic review and meta-analysis

Introduction: Autism spectrum disorder (ASD) is a heterogeneous neurodevelopmental condition increasingly linked to immune dysregulation and chronic low-grade inflammation. Allergic diseases, including asthma, atopic dermatitis, allergic rhinitis and food allergy, are generally associated with immune dysregulation and type 2 inflammatory responses predominantly involving T helper 2-related pathways. Epidemiological evidence also suggests a possible association between ASD and allergic diseases. However, existing studies differ in population characteristics, allergic phenotypes, diagnostic definitions, case ascertainment methods and strategies for confounding control. As a result, the available evidence remains fragmented and the findings are not fully consistent. Therefore, an updated and comprehensive synthesis is needed to integrate observational evidence and examine the associations between multiple allergic diseases and ASD.