Numerous studies have described an altered gut microbiota composition (dysbiosis) in patients with neurodevelopmental disorders that can be correlated with their symptoms, especially gastrointestinal symptoms.

An interventional, randomised, double-blind, placebo-controlled study will be conducted to investigate the effect of a probiotic supplement on the microbiota composition of children aged 3-7 years with neurodevelopmental issues.

The duration of the study will be of 6 months approximately, including 6 months of product intake.

Participants will be randomly assigned to one of the two study groups: control group with placebo administration or probiotic administration group.

Inclusion Criteria:

• Children aged 3 to 7 years old.
• Diagnosed with autism spectrum disorder, according to the clinical criteria of the "Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5)" and who meet criteria for ASD according to the ADOS-2 classification.
• Presenting one or more gastrointestinal symptoms (constipation, diarrhoea, abnormal stools, painful defecation, abdominal pain, reflux, bloating, flatulence).
• Written informed consent signed by the parent or legal guardian with express or tacit consent of the other parent.

Exclusion Criteria:

• With intake of antibiotics in the last month.
• With intake of probiotics in the last two weeks.
• Diagnosed with short bowel syndrome or has undergone relevant surgery on the gastrointestinal tract.
• Exhibiting a defect in the intestinal epithelial barrier (e.g. inflammatory bowel disease (IBD)).
• Diagnosed with endocrinological diseases such as diabetes mellitus, hypo- and hyperthyroidism, Cushing's disease, Addison's disease, etc.
• Having heart failure and a cardiac medical history (e.g. artificial heart valve, medical history of infective endocarditis, rheumatic fever, or cardiac malformation).
• Congenital or acquired immunodeficiency.
• Immunocompromised (e.g., cancer and/or transplant patients taking certain immunosuppressive drugs, patients with inherited diseases that affect or may affect the immune system).
• Uncertainty on the part of the investigator about the willingness or ability of the minor's parents or legal guardian to comply with the requirements of the protocol.
• With oral hyper sensitivity impairments that prevent the uptake of the study product.