This study is about finding special markers in **saliva** that might show if a child has Autism Spectrum Disorder (ASD). **ASD** is a condition that affects how a person communicates and interacts with others. Children ages 18 months to 6 years and 11 months can join. They will have a simple mouth swab for saliva and answer some questions about their health and background. Some children will be checked again later to confirm their ASD diagnosis and learn about any treatments they are receiving.
- **Study Length**: Participation involves multiple visits over time.
- **Non-Invasive Testing**: Only saliva swabs and questionnaires are needed.
- **Eligibility**: Children at risk for ASD and no major health problems can join.
Children must not have certain health conditions like needing a feeding tube, having mouth diseases, or being on or recently taken antibiotics. This study is for kids who doctors think might have ASD, especially if a brother or sister has it too. Joining this study can help doctors find better ways to diagnose ASD earlier and more easily.