Genetic Markers for schizophrenia

We are currently foster parents to a 20 day old male infant. He will be available for adoption shortly. His birth mother has schizo affective and manic disorder, father has manic disorder. First child was taken away at 1 year, and currently has a LOT of problems, currently with different foster parents who do not want to adopt her due to severity of problems. My question is, is there a genetic marker we can test for? What is the likely hood that he would develop these disorders. Is there ANY other testing we can do to accertain wether or not he will be in trouble. We are nearing 50 years old and would love to adopt him, however due to out age, it would be difficult on all of us later in life, if there is a disorder up and merging. Any advise will be appreciated. Thank you