epilepsy and genetics??

Hi, im very new here but ive been wondering if anyone here can help me. My sister and I are twins. we are 24. She has a 5 month old beautiful baby girl. When her baby was born she had to stay in hospital for 3 weeks because she kept on having epileptic seizures, And she had so much seizures that she had to be put on steroids, shes only 5 months old.

The thing is she has Epilepsy and she also cant see properly, and is developing slowly. What does this mean? They said the cause was that my sister had this gene (What gene? i dont really know) but so did her husband, and his was much more dominant or something.
Does this mean she wont grow up to be a normal little girl? does this mean her mental ability will develop slowly liike she will be mentally disabled god forbid? will she never see properly again? and also, Would I have this gene as well?

Im really sad for my twin sister, i love her and her baby very much, i cry all the time, I dont understand what excatly is going on, so if any dr or anybody, who would have any knowledge or information about this please dont hesitate to write to me. I greatly appreciate it.

Thankyou

[Lisa Kessler, MS, CGC]

I am sorry that your young niece is going through so much.  It may help for your sister to request a copy of the genetic testing report that was performed on her daughter.   In order to learn more about what having this gene change means for your niece, it may help her to meet with a genetic counselor and pediatric geneticist.  A geneticist can be found through the American College of Medical Genetics, and a genetic counselor can be found through the National Society of Genetic Counselors.   You also asked an important question about your risks to carry a copy of the changed gene.  In order to answer this question, you may benefit from meeting with the genetic counselor as well.  You would need a copy of the testing that your sister and her family had in order for the appointment to be most helpful for you.   Best wishes to you and your family.