The purpose of this study is to accumulate and quantitatively analyze data on the microbiome, serotonin signaling and genetics, and inflammatory cytokines from patients with Autism Spectrum Disorder and Fragile X Syndrome. Computational analysis of multi-dimensional datasets will be used to establish a "Diagnostic and Therapeutic Index" - an objective set of tools that can help differentiate subtypes of Autism Spectrum Disorder and develop more accurate methods of diagnosis and response to treatment.

Inclusion Criteria:

• Early childhood (pre-diagnosis) OR existing ASD diagnosis (Moderate to Severe)
• Existing FXS diagnosis

Exclusion Criteria:

• Hospitalization
• Enrolled in another clinical study

Autism Spectrum Disorder (ASD) and Fragile X Syndrome are neurodevelopmental disorders characterized by repetitive behavioral patterns, hypersensitivity, and persistent deficits in social communication. ASD is currently diagnosed exclusively on the basis of neurobehavioral patterning - an approach that (1) cannot distinguish subtle differences between ASD subtypes, (2) is subject to observer bias, and (3) introduces uncertainty regarding root causes and response to treatments. Developmental disorders are often accompanied by various co-occurring medical conditions like gastrointestinal dysfunction or anemia, which can be leveraged to sub-segment the autisms spectrum and improve diagnostics and treatment. Further investigation is needed to define the degree to which specific comorbidities contribute to behavioral symptomology.