In the case of monogenic disorders our work in the PGD laboratory often uses linked DNA markers to distinguish 'healthy' from affected embryos. To find out which markers we should use we compare healthy and affected individuals within the family from at least two generations.
- To do this we therefore need your samples (from the prospective parents) and also samples from the parents of the prospective parent who is affected or a carrier, or from your children.
- Sometimes (we also) ask for blood or DNA samples from brothers and sisters, or a DNA sample from chorionic villus sampling or amniocentesis or from a fetus after a terminated pregnancy.
- Finally a semen sample is sometimes requested for marker tests if this is necessary. Each of the requested samples (except semen samples) must be accompanied by a laboratory report (a 'protocol'), indicating whether the mutation is present or absent.
Once found, the DNA markers that can distinguish healthy family members from those who are 'sick' or 'carriers' are referred to as informative markers. These allow us to make an efficient and reliable diagnosis on the basis of the embryo cells.