huntkc at gmail.com
Wed Jan 5 15:45:50 GMT 2022
On Wed, Jan 5, 2022 at 9:53 AM quietann <quietann at gmail.com> wrote:
> Testing for Tay-Sachs is a simple test, and recessive disease (need two
> copies of the gene to be affected.) In a few Jewish communities, people
> will be tested as they reach the age of marriage, and revealing "carrier
> status" is part of the shidduch (matchmaking) to be sure that 2 carriers
> don't marry each other. Simple recessive diseases like this (cystic
> fibrosis is another example) have virtually error-free tests. Tay-Sachs is
> a horrible horrible way to die. It is degenerative, and children affected
> are usually dead by age 4, and their short lives are miserable. There is no
> cure, and really no treatment to speak of. But I know what you want
> to force on people.
One small adjustment. Cystic Fibrosis is considerably more difficult to
test for than Tay-Sachs or Sickle-Cell - false positives are unlikely, but
false negatives are pretty common.
The core problem is that there are over a thousand different mutations that
can produce CF, and the widely-available tests look for only the most
common variants. (As a side-note, the old sweat test only catches 80% of CF
cases, so the genetic tests do much better than that one ever did,
I had a (very expensive) full test for it where they actually completely
sequence the gene and check it against all the known variants (test given
after I tested negative for a second time and there was uncertainty about
whether it was correct).
As a result, I know that I do not have CF or any of several other
lung-affecting genetic diseases, so the current theory is that my lung
troubles are entirely due to the bad luck of getting a rare and nasty
chicken pox complication when I was 12 (MRSA pneumonia - staph isn't that
rare after chicken pox, but MRSA was really unexpected in the 70s) followed
by slowly getting worse as pneumonia incidents pile up.
For a particular case, there's the tale of what happened to a friend: when
he married, they tested his wife for the standard top-5 variants, and she
was clear. Testing stopped there. If they'd tried harder, they would have
discovered that he's a carrier of the most common variant - F50del if you
like fancy terminology - and she's a carrier for one of the rare ones.
Their first son has CF and almost died shortly after birth. His condition
is only partially treated by the new trikafta drug (it only fixes people
with that most common variant, so it only partially fixes his situation).
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