A Mistake that is Not a Mistake/ a Reason for It

     In my novel, American Boys, there is one purposeful inaccuracy.  In the book, Lizzy has two sons, one with retinitis pigmentosa (RP), and one with autism.
     I know that, because I have RP, my father had it, and my sons both have it, that it is passed from father to daughter, and daughter to son, so Lizzy's sons would both have RP, if one had it, but I could be wrong, because I have also heard it is a 50/50 genetic possibility.  On the other hand, I have read that sons always inherit it from mothers, and daughters from fathers, so that if I had a girl, she would not have it.  
     The reason I decided to write it this way, is that first of all, it is fiction, so it does not have to be accurate to the T, but the thing is, even though we all have it, my sons and me, as well, I wanted their lives to be easier than ours.  The younger boy has a seizure disorder, and my older son had a seizure disorder when he was twelve, and my younger son has asthma.  So, I guess I was trying to make parallels, but wanted it to be palatable.  I mean, it is hard for me to tell people the truth of my own life, because I hate pity, and I hate people to think of my life as too hard, because to me it is just a life, and I am not the only one effected.  The kids are.
     Some day, but probably not, I will write my own exact story, but I doubt it, because writing about my own story makes me sad somehow, so making fictional characters, with parts of my problems, made it go down easier, for the reader.  At least that was my angle.
     Possibly, but I doubt it, there could be some other weird gene pattern where my story's character, Daniel, could be the only one with RP in the family, and I guess it happens, but him having a brother, I highly doubt it.  Also, usually the mother would have it, if she carried it.  That is the usual way it works.  Father to daughter, daughter to son, or mother to son.