Autism and developmental delay are complex disorders with both genetic and non-genetic causes. About 10% of people with autism have a genetic condition that may or may not be inherited. There are numerous genetic conditions that can cause autism and/or developmental delay, including certain chromosome abnormalities and Fragile X syndrome.
We recommend that your son meet with a clinical geneticist for evaluation. A clinical geneticist can perform a detailed physical exam and may order tests to help determine if there is a genetic cause for your son's behaviours and problems. This information may be informative to other family members, especially your daughter. A medical geneticist can be found at the American College of Medical Genetics website.
We recommend that your daughter and her husband meet with a genetic counselor, who can assess risk based on ethnicity, personal and family history and discuss appropriate testing options. A genetic counselor can be found at the National Society of Genetic Counselors website or through companies like mine, AccessDNA. Best wishes to you and your family.