I am looking for info on the test that determines if you are carrier for
CF. Is it a PCR based test? If you know the reference for the journal
article on this could you point it out to me? Also, if anyone has any
insight on if if is helpful to know that a newborn has a 25 % chance of
having CF or not (ie, if early diagnosis is helpful, etc). Thank you.

There is a PCR based diagnostic test for looking at the CF
carrier status.  Unfortunately, there are many mutations of the
CF gene and since it is a large gene, it is difficult to
identify all mutations.  As of now we don't know all possible
mutations that can cause CF so they can't all be screened.  The
most common, `delta 508' is present in about 70% of carriers
however that means only half of the CF patients are pure `delta
508s.'

The usual way the test is done in a clinical setting is in the
case of a family with a CF child.  The parents are tested to
see if their individual CF mutations can be identified.
Different labs that test for CF will perform it different
ways.  Here at UVa we screen with a panel of primers that pick
up `delta 508' and a few others.  We can maybe identify the
carrier status of 85%.  Depending on the ethnic background,
other mutations may be looked for (I believe there is a
mutation more common in Jewish individuals).  If both parents
can be identified, then we can inform the parents that with
their next pregnancy we could determine if the fetus carries
both mutations.

After that it's up to parents to decide.

With regard to your statement, once parents have a chld with
CF, then their chances with each succeeding pregnancy are
always 25%.

Mike Kurilla