Genetic Testing
  • The gene that codes for CFTR was sequenced in 1989, which led to the possibility of genetic testing, identifying the abnormal gene in the DNA of any cells
  • This has paved the way for genetic screening to confirm the results of conventional tests, to identify carriers and also to diagnose CF in an embryo
  • Genetic testing can be performed on any DNA, so it's possible to take samples from cheek cells, white blood cells or cells from a foetus or embryo
  • The DNA is tested to see whether it contains the known base sequences for the most common mutations that cause CF
Haw can Genetic Screening be Used?:
To confirm a diagnosis:
  • Genetic testing can confirm the diagnosis of CF, however, since there are a large number of different mutations of the CFTR gene which cause the disease, a negative result should be treated with caution
  • It's not currently feasible to test for all the hundreds of possible mutations that lead to CF
To identify carriers:
  • Genetic testing can confirm carriers - a cell sample is takend and used to detect abnormal alleles in people without the disease who are heterozygous
  • Where there's been a history of CF in the family can be of value in assessing the probability of having a child with the disease
For testing embryos:
  • There are two techniques to obtain samples from an embryo - the more common is amniocentesis
  • This involves inserting a needle into the amniotic fluid to collects cells that have fallen of the placenta and foetus
  • This can be carried out at around 15-17 weeks of pregnancy, involving a riks of miscarriage of between 0.5% and 1%
  • Chronic villus sampling (CVS) is the second method - a small sample of placental tissue (incl from the foetus) is removed, either through the wall of the abdomen or through the vagina
  • THis can be carried out earlier, between 8-12 weeks, but carries a risk of about 1-2% of inducing miscarriage
Testing before implantation (PIGD):
  • Genetic testing can enable per-implantation genetic diagnosis (PIGD)
  • When carrying out in vitro fertilisation (IVF), it's possible to test an embryo before it has implanted in the uterus
  • A cell can be removed from an embryo growing in culture when it has only 8 or 16 cells without harming an embryo
  • The DNA of the cell can be analysed and the results used to decide whether to place the embryo into the womb

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