I have this condition and it is hereditory, if the carrier has children they have a 50% chance of getting it. Me and my sister are both carriers.

Im the only one in my family that has it i have 1 brother and 1 sister and neither of them have it. we are not sure where i got mine from. my mother carried all of us fine and i seem to be the only one in our family that has it. how can this be? my moms parents had 10 kids and my dads parents had 5 kids. im so confused about this.