Fecal Microbiota Transplantation in Children With ASD

Inclusion Criteria: * Aged 3-16 years. * Diagnosed with ASD according to the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5), with a Childhood Autism Rating Scale (CARS) total score ≥36 (moderate-to-severe autism). * Legal guardians fully comprehend the trial's informed consent and voluntarily provide written consent. * Compliance with follow-up visits, examinations, and specimen collection. * No probiotic supplements consumed within the preceding 3 months. Exclusion Criteria: * Use of probiotics or prebiotics within 3 months prior to enrollment. * Antibiotic usage within 1 month prior to enrollment. * Presence of fever (axillary temperature ≥37.5°C). * Dependency on tube feeding. * Severe gastrointestinal conditions requiring immediate intervention (e.g., life-threatening intestinal obstruction, perforation, hemorrhage, ulcerative colitis, Crohn's disease, celiac disease, or eosinophilic esophagitis). * Diagnosis of severe malnutrition, underweight status (BMI-for-age \<3rd percentile), or severe immunodeficiency disorders. * History of severe allergic reactions (e.g., anaphylaxis). * Monogenic disorders (e.g., Fragile X syndrome, Rett syndrome). * Comorbid psychiatric diagnoses, including depression, developmental speech/language disorders, intellectual disability, attention-deficit/hyperactivity disorder (ADHD), selective mutism, reactive attachment disorder, or childhood schizophrenia.