There are several PGD testing techniques that Melbourne IVF use to test embryos. Your individual circumstances will determine which test is most appropriate for your embryos, and your PGD Fertility Specialist will discuss this with you.
Testing for chromosome errors
A human cell contains genetic material arranged in dense strands, called chromosomes. A normal cell will contain 23 pairs of chromosomes. If the cells of an embryo contain the wrong number of chromosomes, a condition known as aneuploidy, this will usually result in death of the embryo at a very early stage.
It is thought that aneuploidy is responsible for many cases of implantation failure and recurrent miscarriage (both of these conditions are very common in human reproduction, not just in IVF patients). As women get older aneuploidy increases in their eggs and this is transmitted to their embryos.
In some people, pieces of chromosomes have broken off and attached themselves onto the ends of other chromosomes. These people have a normal amount of chromosome material (known as balanced translocation), but their offspring may inherit only the chromosome with one portion missing, or the chromosome with an extra portion added (unbalanced translocation). Embryos with unbalanced translocations are usually non-viable, and an unbalanced translocation will result in infertility, implantation failure, or miscarriage (or rarely the birth of a baby with severe abnormalities).
FISH (Fluorescent In-Situ Hybridisation) is a technique for counting the number of some chromosomes in a cell.
FISH for aneuploidy: For implantation failure, recurrent miscarriage or advanced maternal age, FISH may be used to look at 8 chromosomes (usually number 4, 13, 16, 18, 21 22, X & Y).
FISH for translocations: In most, but not all cases of translocation, it is possible to design a FISH test that will detect the presence of an unbalanced translocation by embryo biopsy. The test must be specially designed for each couple to match breaks in the chromosomes and this may take some time and effort.
FISH for gender selection: Some genetic conditions affect one gender, for example haemophilia and muscular dystrophy. Where there is a medical reason such haemophilia, the FISH technique can be used to determine the gender of the embryos. Only embryos of the unaffected gender (or less severely affected, or less likely to be affected) by the disease will be transferred.
Gender selection for family balancing is not legal in Victoria and is therefore not available.
Melbourne IVF specifically developed Single Gene disorder tests:
A gene is a sequence of DNA (genetic material) on a chromosome with a particular function (humans have up to 20,000 different genes, arranged on 23 pairs of chromosomes). When the DNA sequence on a particular gene is altered, a genetic disorder such as cystic fibrosis or thalassaemia may result. It is now possible to test for many hundreds of single gene disorders by pre-implantation genetic diagnosis.
A patient-specific test is used to determine which embryos have the normal (healthy) gene, and which have the abnormal gene, in the particular genetic condition being tested for.
This test usually includes a method to directly detect the gene alteration (mutation) that is associated with the disease, as well as genetic markers that track the mutation and provide extra certainty.
As these tests are couple-specific, they can take some time and effort to design and establish.
It is now possible to test for a very large number of single gene disorders by preimplantation genetic diagnosis. Worldwide hundreds of genetic disorders have been diagnosed by PGD. Melbourne IVF has now developed tests for over 40 genetic disorders, and many more tests are in progress. Some of the most common conditions tested for are:
Huntington disease (direct and exclusion)
Cystic fibrosis
β-thalassaemia
Duchenne muscular dystrophy
Fragile–X
BRCA1 / BRCA2 (hereditary breast / ovarian cancer)
If you would like further information about what other single gene tests are available, email the PGD team at pgd@mivf.com.au.