Re: preemies? (genetic testing)

[Guest guest]

--- In Listen-Up , " daisybloodflower2002 " > We still

haven't found out however if this or anything else has

> caused my sons deafness. He is getting an MRI on the 27th to rule

> out any brain/skull injuries, tumors, etc. We have also been

> referred to get genetic testing. However my husband and I don't

have

> any family history of deafness as far back as can be remembered.

The

> only deaf person we have in our family is a cousins son who had

> meningitis when he was young.

Same in our family -- no one remembers any deaf relatives, and for

my husband's dad's side of the family, there is an extensive

geneaology. BUT, it turns out my hearing husband and I both carry a

recessive mutant gene for connexin-26, which when paired with a good

copy causes no hearing loss. Put two of these mutant genes

together, though, and you get hearing loss. My husband and I also

have the same kind of connexin-26 mutation (35delG) which usually

causes the most severe-profound loss. The mutation rate in the

European population (what fraction of people carry this mutant gene)

is about 1 in 50, a little more common in the Mediterranean area

(1:35). So 50 x 50 = 2500. Thus, there is a 1 in 2500 chance that

two hearing people of European origin will meet and have the

potential to have a hearing impaired child. Then, each child has a

1 out of 4 chance of being hearing impaired because the parents have

those good, dominant copies of connexin-26. The mutation can

persist in blood lines for generations before it shows up.

> It still is very difficult to try and understand why some kids are

> born with hearing loss. I am told that quite often it can never be

> explained.

I was also told that we may never learn why our child has a hearing

loss, but then we moved to Boston. The researchers at the

Children's Hospital here are really interested in learning about the

genetics of deafness. I have met quite a few families of kids with

connexin-26-related hearing loss. One year, of the 7 kids in my

son's class, at least 3 were hearing impaired due to connexin-26.

That seems like kind-of a lot to me -- almost half the class just

due to one gene. (As for the other kids, two had other causes and

the other two weren't tested.)

I have also spoken with one of the research geneticists at

Children's/Harvard Med, and she said that most of the causes of

recessive hereditary deafness are known, and they test for all of

the 6 or 7 common ones. I think with time, the reasons for hearing

loss will become less and less mysterious.

Lydia

, almost 8, deaf CI user

Colin, 11, hearing