Hi, concerned twin sis, As Dave and Chris said there is no known prevention for schizophrenia nor predictive  knowledge of who exactly might go on to develop it over a lifetime. Apart from the genetic risk which you obviously share with your sister, outside factors ,early neonatal damage,stresses ,drugs ,nurturing differences,as a child and later, and many unknown triggers are also probably involved. So we are all different, with a unique precious individuality, even identical twins, as you of course so well know and value, and we need to be!! Vive la difference! To answer at a slight tangent to your question, the very fact you ask it shows your insight and family experience would alert you to signs in yourself at an early stage, should you be unlucky  and also go on to develop sz. Your preknowledge would give you a great advantage compared with someone else to try and get early help and treatment.....not prevention exactly but known to be connected with much improved term outcome. Good luck, Chris,  (mother, and retired doc)