My parents were cousins & my brother had down syndrome. now i am too getting married to my cousin soon, are there any birth defect risks in our future babies, how to prevent those risks ?

Prevent=don't marry: Down syndrome is a random event & has nothing to do with their cousin status. We each have recessive genes to an estimated 3-5 potential metabolic problem like PKU and the closer a kinship, the more chance an offspring from that pairing would have a recessive genetic disease. This is highest if a parent fathers a child with a daughter, and the risk declines the further away the relationship goes

Reconsider?: I agree with Dr. Ferguson. Marrying one's cousin definitely brings increased genetic risks to off spring.