PGD was originally proposed for couples at risk of having a child affected by severe genetic disorders such as cystic fibrosis, which manifest themselves at birth or in very early childhood. However, it is now possible to test for some diseases that occur at a later stage in life, such as Huntington's disease and some hereditary cancers. "Because the child will carry only a risk - albeit it a high one - of developing these conditions during adulthood, many parents, as well as clinicians, have doubts about terminating such a pregnancy," Professor Viville says. "In fact some couples would prefer not to have children in these circumstances."
Twelve couples with a risk of passing on FAP to any children were referred to Professor Viville and his team between 2000 and 2005. At first the team worked on tests to detect the most common FAP mutation, but then, by carrying out double and triple diagnostic tests on each cell, were able to detect the many rarer mutations that are involved in familial cases. "Because the pathology is dominant, and only one member of the couple is affected and at risk of transmitting the disease," said Professor Viville, "we only have to look for one mutation at a time.
"But there are a number of these mutations and therefore it is necessary to develop a different test for each if we are to be sure that PGD will be effective. Our test is very robust as well as being technically innovative - for the first time in this disease we have been able to use molecular technology at the single cell level, which allows us to detect mutations that are otherwise very difficult to identify."
The team started eleven IVF cycles, of which nine gave rise to embryo biopsy and eight had an embryo transfer. From these, one boy has been born and two other pregnancies are on-going. Reanalysis of eleven un-transferred embryos confirmed PGD results for FAP mutations.
"We are now able to propose PGD to most couples at risk of transmitting a familial form of FAP to their children", says Professor Viville. "With our experience growing all the time, we hope that we will shortly be able to develop new protocols which will enable us to offer PGD for all mutations involved in FAP, including those which occur for the first time."