Pre-implantation tissue typing ('saviour siblings')
What is pre-implantation tissue typing?
For children with life-limiting blood disorders such as beta thalassaemia, Fanconi’s anaemia and Diamond Blackfan anaemia, one of the best available treatments is a transfusion of stem cells from cord blood provided by a tissue-matched donor.
Preimplantation tissue typing (PTT) offers parents the chance of conceiving a child who is a tissue match with their older sibling. Using a tissue-matched donor who is a close relative of the recipient often means that treatment is more likely to be successful than using a tissue-matched unrelated donor.
In the media, those born following this procedure have sometimes been referred to as ‘saviour siblings’.
Is preimplantation tissue typing for my family?
You should talk to your child’s treating clinician about whether PTT is an appropriate option for you. It may be suggested as an option if:
- your child has a life-limiting blood disorder that can only be treated through a donation from a compatible donor
- there are no closely related compatible donors available in your family and your clinician has established that an unrelated donation from a tissue bank would not be suitable
- the condition your child suffers from has an established genetic basis and you also want to ensure that any future children you have do not inherit the condition.
How does PTT work?
PTT uses the same technique as preimplantation genetic diagnosis (PGD), but involves testing the tissue type of the embryo.
In many cases, the condition the existing child suffers from is heritable, meaning it can be passed from generation to generation. In these cases, parents can use PTT with a PGD step, to ensure they have a child who is not only a tissue donor for the older sibling, but is also born free from the condition.
In some cases the condition can occur where there is no genetic history in the family. An example of this is Diamond Blackfan Anaemia. In such cases, tissue typing can be carried out without the additional PGD step.
Which conditions can be tested for using preimplantation tissue typing?
For a complete list of licensed conditions (the conditions for which preimplantation tissue typing has been previously licensed are noted with an asterisk):
Though these conditions have already been authorised for PTT in particular cases, each subsequent case must still be approved by the HFEA. Your PGD clinician will manage this process for you. If the condition has already been approved either for PGD alone or for PTT with PTT, these application are fast-tracked as quickly as possible
If, however, the condition is one which has never been authorised by the HFEA either for PGD, for PGD with PTT or for PTT alone, the process is different and will take longer.
Which clinics carry out PGD?
Clinics licensed to carry out PGD may also carry out preimplantation tissue typing. Not all PGD clinics, however, will offer this treatment.
Some clinics will have particular experience of testing for some conditions.
To find clinics in the United Kingdom that are licensed for PGD, and the tests they have experience in, visit ‘Choose a Fertility Clinic’
What are the risks of preimplantation tissue typing?
The risks of preimplantation tissue typing are similar to the risks of IVF, and PGD.
There is also the risk that the donation does not successfully treat the child.
We advise that you speak to your treating clinician about the potential risks.
What is the chance of having a baby with preimplantation tissue typing?
It is difficult to assess reliable success rates for PTT because there is very little data available.
In the case of PTT the numbers of cycles every year are even smaller than for PGD, making it more difficult to assess the chances of success.
As with most fertility treatment, success will depend on many factors, including the woman’s age and whether a form of infertility has been identified.
The measure of success for PTT will not only be the birth of a baby free from the condition, but whether a transfusion of stem cells from that baby will help to treat the older sibling. Data regarding the success of this kind of treatment also remains very limited, and we strongly recommend you speak to your child’s treating clinician about your chances of success.
Patient support groups
Many people find it helps to speak with those who have gone through similar experiences. There are patient support groups for people with children suffering from some of the conditions for which PTT may be an option:
Fanconi Hope is the charity which supports the The UK and Ireland Fanconi Anaemia Family and Clinical Network to promote research into Fanconi’s Anaemia and provide information for Fanconi’s Anaemia families.
DBA UK is a charity which provides patient and family support for those affected by Diamond Blackfan Anaemia in the UK
UK Thalassaemia Society
The UK Thalassaemia society provides information, education and research for those affected by, or working with thalassaemias.
Genetic Alliance UK
Genetic Alliance UK (formerly Genetic Interest Group) is the national charity of over 130 patient organisations supporting all those affected by genetic conditions. Genetic Alliance UK provides a range of patient information, including leaflets on cord blood banking.
There have been three separate reviews of HFEA’s policies towards preimplantation tissue typing. The reviews, carried out in 2001, 2004 and 2009, have covered the HFEA’s approach to PTT licensing.
Page last updated: 01 April 2014