Can we detect whether our unborn child will be deaf or dumb?

Q: My wife's parents are deaf and dumb. Her father was affected since his mother suffered from chicken pox during pregnancy. My wife's mother on the other hand is deaf and dumb by birth, for no apparent reason. Me and my wife are both normal. Interestingly her younger sister is also deaf and dumb. Now my wife is 3 and a half months pregnant. She is anxious to find whether our child will also suffer the same impairment? Are there any tests to detect hearing ability of the fetus? I have heard something about X chromosome test. Are they of any help?

A:Most often genetic deafness is due to autosomal recessive genes, and not the X chromosome. Three genes can be tested, the commonest of which is connexin 26 gene. The best approach in this case would be to test your sister for connexin 26 gene mutations, and if mutations were found, then check the pregnant lady.As there are many genes that can cause deafness the couple should see a geneticist along with the sister who has deafness, to answer their specific questions.