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Hello and thank you for using JustAnswer. I definitely understand your concern regarding this situation, but I also want to reassure you concerning one thing that the risk of your fiance getting Schizophrenia is 5-10 percent, not 15 percent. This is what longitudinal research has shown based on the fact that your fiance's mother and possibly her grand-father may have had it (but if her grand-father started to act odd in his later years than it could have been psychosis related to dementia). But as of right now the risk is 5-10 percent. Also given that your fiance is 25 years old with no manifestations of the disorder is a good sign as the average age for women manifesting Schizophrenia is 25 years old, so every year from now until she reaches 30 the chance of Schizophrenia lessens. After 30 years old the chance of Schizophrenia is very low to the less than 1 percent variable that every individual shares, so statistically she would be no different than you or I.
I believe you should not end the relationship based on this possibility that she may develop Schizophrenia and as of right now it is a very low possibility where there is a 90-95 percent chance she is not going to manifest any symptoms of this disorder. It is true that even with medications the well being of a person with Schizophrenia is diminished and most of them cannot lead a well adjusted life because of the symptoms and the side effects of the medications, but your family is concerned about a really low chance of her getting this disease. I know your family has your best interests at heart, but I also think they are biased here just by the name "schizophrenia" and are not quite looking at this logically...you can listen to your friends and family, but the decision is up to you on the risk and benefits. At this point I think the benefits of a good marriage with someone you love outweigh the potential 5-10 percent risk, which like I said will lessen every year until after 30 years of age where he likelihood of developing Schizophrenia will be the same as yours and every other person on the planet.
Lastly you asked if there was any way to prevent the risk of developing Schizophrenia, unfortunately there is not and that is because we are not even sure what causes this disorder, so we have no way of preventing it or curing it at this time.
I hope this helps to give you a different perspective and I truly wish you all the best no matter what you decide.
I hope this answers your questions and gives you some guidance on this issue. Please let me know if you have any questions or concerns as I am happy to assist and support you regarding this issue.
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