by Neil Bauman, Ph.D.
A mother wrote,
My daughter has LVAS [Large Vestibular Aqueduct Syndrome]. My husband and I have not had genetic testing done to determine whether we are carriers. Am I to assume that since my daughter has LVAS, so will my son?
No—unless you both also have LVAS. The fact that your daughter has LVAS indicates that you both are carriers of the LVAS gene(s). Since you are just carriers, then there is a 25% chance your son will have LVAS, a 50% chance he will be a carrier, and a 25% chance he won’t carry the gene(s) at all. At least that is how I understand it. (I’m sure it is more complicated than the above because they don’t even know all the genes involved in LVAS yet—but it should give you a good general idea.)
Also, remember this is the average in a large population. That said, it IS possible you could have 4 kids in a row with LVAS, or have 4 kids in a row without LVAS—but on the average the 25, 50, 25 rule holds—just like you can flip a coin and get 4 heads in a row or 4 tails in a row—but it is not likely.
Just because you already have a child with LVAS doesn’t make succeeding children more (or less) likely to have LVAS. each child has the same 25/50/25 percent chance of having LVAS independent of whatever has occurred before with your other children.