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Pre-implantation tissue typing (PTT)

Pre-implantation tissue typing (PTT), also known as ‘saviour siblings’, is a technology which can be used in some cases to help children with very serious blood disorders. Find out more about PTT, the risks and whether it might be right for your family.

What is pre-implantation tissue typing?

PTT is a type of embryo testing which can be used in the treatment of children with life-limiting blood disorders such as beta thalassaemia, Fanconi’s anaemia and Diamond Blackfan anaemia.

The best available treatment for children with these illnesses usually involves a transfusion of stem cells from a tissue-matched donor, ideally a close relative. Where a close relative isn’t available, parents can choose to have another child and use PTT treatment to only select embryos that are an exact tissue match to their older sibling. It’s for this reason that PTT is sometimes referred to as ‘saviour siblings’ technology.

Is PTT right for my family?

You should talk to your child’s doctor about whether PTT is appropriate 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 tissue-matched donor
  • there are no tissue-matched donors available in your family and your doctor has confirmed that an unrelated donation from a tissue bank would not be suitable
  • the condition your child suffers from is genetic and you want to ensure any future children you have do not inherit the condition.

How does PTT work?

PTT is very similar to another type of embryo testing called pre-implantation genetic testing for monogenic disorders (PGT-M) (previously known as pre-implantation genetic diagnosis PGD). The main difference is that in PGT-M you’re testing embryos for genetic diseases (so you can choose one that doesn’t have the disease) whereas in PTT you’re selecting embryos that are a tissue match.

Find out more about the PGT-M process

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 PGT-M, to ensure they have a child who is no

Which conditions can be tested for using PTT?

PTT can test for serious blood disorders including Sickle Cell Anaemia and Wiscott-Aldrich Syndrome.

View the full list of conditions you can test for

What if my child’s condition hasn’t been approved for PTT?

If there’s a condition you’d like to be able to test for that hasn’t already been approved, your clinic will need to apply to us to add it to the PTT list. There are strict criteria for deciding which conditions can be permitted so bear in mind it could be a lengthy process and you may not be successful.

If a condition has already been approved for PGT-M testing or PGT-M with PTT (but not for PTT on its own), your application will be considered as quickly as possible.

How safe is PTT?

So far, the evidence we have shows that PTT is safe for both mother and baby. However, it’s performed so rarely in comparison to other treatments we have much less evidence on the risks.

There are risks from having IVF

Find out more about the risks of IVF.

Bear in mind no treatment is 100% effective. You might successfully give birth to a child who’s a tissue-match for your existing child but then the donation doesn't work. Also, some embryos may be damaged by the process, which means they would need to be discarded. Make sure you discuss all the potential risks with your specialist before treatment.

How can I get PTT treatment?

The first step should be talking to your GP or specialist. It may be possible to have treatment on the NHS but it will depend on what’s offered by your local clinical commissioning group (the body responsible for providing NHS services in your area).

Only very specialist clinics provide PTT. You’ll need to first find a clinic that offers pre-implantation genetic diagnosis (PGT-M) and contact them to see if they also offer PTT.

Find clinics that offer PGT-M in your area

How successful is PTT?

As with all fertility treatments, the woman’s age has a big impact on her chances of having a baby.

The measure of success for PTT will not only be the birth of a baby free from the condition, but also whether a donation of stem cells from that baby successfully treats the older sibling. Unfortunately this treatment is performed so rarely we simply don’t have enough data to provide reliable figures on this. We strongly recommend you talk to your child’s doctor about your personal chances of success. Are there any support groups I can talk to?

Are there any support groups I can talk to?

Many people find it helpful to meet other families who have had similar experiences and have some understanding of what they’re going through. The below are patient support groups for people with children suffering from some of the conditions treated by PTT.

Fanconi Hope
Fanconi Hope is a national charity supporting those affected by Fanconi Anaemia, a rare genetic disorder which causes bone marrow failure.

DBA UK is a charity providing 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 is a national charity of over 130 patient organisations supporting all those affected by genetic conditions. Genetic Alliance UK provides a wide range of patient information, including leaflets on cord blood banking.

Review date: 27 June 2026