Screening for cystic fibrosis carriers
by Peter
Lavelle
Published 01/12/2005
Every year 70 babies are born in Australia with cystic fibrosis. The
child suffers serious lung and digestive problems - they don't manufacture
a vital protein, which causes secretions to become very sticky and their
lungs and pancreas to literally 'gum up'. The lungs become susceptible to
infection and digestion doesn't work propery.
Treatment is much more effective than it was 20 years ago. Most
children with cystic fibrosis now can expect to survive into adulthood.
But the average life expectancy is still only in the mid thirties.
Cystic fibrosis is an inherited condition, but a child has to have an
abnormal gene from both parents to get it. When both parents are
'carriers' of the abnormal gene, there is a one in four chance of this
happening.
About one person in 25 in Australia is a carrier. About one in 2,500
kids will be born with the condition.
At the moment, carriers aren't identified by testing. Instead, newborn
babies are routinely screened for the condition (that's how most new cases
are diagnosed). Only then do most parents become aware they are carriers.
Parents are then routinely offered prenatal testing of a foetus in any
subsequent pregnancy and they have the option of then terminating that
pregnancy. But it's too late to do anything about the first child.
There is a test to identify carriers of a cystic fibrosis gene. It's
fairly reliable (with an 85 per cent accuracy rate), and it involves a
painless cheek swab. But it's generally not offered to Australian couples
unless there's a family history of the condition. The trouble is, most
carriers don't know they are carriers, and have no history of the
condition. The faulty gene has been hidden away in their ancestry, not
expressed.
A group of doctors from the Royal Children's Hospital, Melbourne,
writing in the latest edition of the Medical Journal of Australia,
say testing for carriers should be more widely available.
The doctors propose that the genetic test be offered as a prenatal test
early in pregnancy. The couple would both be tested, and if they were both
carriers, the foetus would be tested (via chorionic villus sampling, in
which a portion of the placenta is sampled). If the foetus had both
mutations (a one in four chance), the parents could then be given the
option of terminating the pregnancy.
Ideally, the researchers say, carrier screening should be offered to
partners before they conceive. Couples could be tested for carrier status,
and if both partners were carriers, they could consider whether they want
to conceive in the first place. If they did, they would have the option of
conceiving and terminating the pregnancy if the foetus had both mutations.
Or they could opt for in-vitro fertilisation - with the embryo conceived
and tested in the lab, and only implanted in the woman's uterus if it was
found not to have both mutations.
There is a successful carrier screening program for cystic fibrosis
that's been operating along these lines in Edinburgh, Scotland, which has
halved the incidence of cystic fibrosis in that community, the researchers
say.
At the very least, they argue, it should be offered as part of routine
prenatal testing, like screening for Down's syndrome. The doctors say it
should be funded by Medicare, on the grounds of cost-effectiveness (saving
the resources otherwise spent treating a child with the condition) and
prevention of future suffering for kids and their
families.
