Suppose your parents have a baby and you now have a new baby sister.  Suppose when your mother and father were born, tumors developed on their nerves called neurofibromas.  If so, they had a genetic disorder called Neurofibromatosis.  Around age one, your baby sister also develops this disease.  She has surgery on her nerves and becomes deaf because doctors have to remove the auditory nerves.  Doctors are trying to come up with ways to help children’s hearing return.  Because your sister, mother, and father have Neurofibromatosis, your children may develop it, also.