Development of the PGD test
As soon as the CMG has all the necessary reports and samples and has identified the genetic abnormality, the development of the PGD test begins. The aim of this is to obtain a reliable genetic diagnosis on one or more cells from an embryo.
The time taken to develop the PGD test varies at present from a few weeks – for common indications – to eight months or longer – in rare or new indications.
What types of PGD tests are available?
- In monogenetic disorders the PGD test can detect an abnormality on one gene.
- In chromosomal abnormalities the test serves to detect abnormalities on the chromosomes (number, structure). We can:
- count (particular) chromosomes, or
- look at the structure of the chromosomes. We do this to analyse the normal/balanced segregation pattern in chromosome translocations.
- In X-linked disorders, thanks to the PGD test we can determine the gender of the embryos. Then depending on the disorder only female or only male embryos can be considered for return to the uterus.
In most X-linked disorders we are however able to perform a mutation-specific analysis and thus return both healthy male and female embryos.
- Another type of PGD is HLA typing. This special PGD test examines which embryos have the same tissue type as an existing, seriously ill child of the same parents.
Children with a particular (fatal) blood or immune system disorder can sometimes be cured by a blood and marrow stem cell transplant. That is only possible if the transplanted cells are HLA compatible with the cells of the sick child. If they are not compatible, then they are rejected. In other words a baby born from an HLA treatment can be a donor to save a sick brother or sister.
Such a baby is also called a ‘saviour baby’ or ‘donor baby’ in the media.