SAVIOUR SIBLING PROGRAMME AND DIRECT HLA TYPING FACT SHEETShearn
WHAT IS BETA THALASSEMIA?
Beta thalassemia is a genetic blood condition whereby the body produces less haemoglobin, an iron-rich protein in red blood cells that carries oxygen to all parts of the body. Beta thalassemia occurs most frequently in people from Mediterranean countries, Middle East and Central Asia.
Beta thalassemia major is the beta most severe form of thalassemia, it is caused by two copies of mutated HBB gene.
If it is left untreated, the affected child may have an enlarged spleen, liver and heart. Their bones may also become thin. Symptoms usually develop in the first 2 years of life. They may have:
- Life threatening anemia (cooley’s Anemia)
- Delayed growth
- Developed yellowing of the skin & white of the eyes (jaundice)
- Enlarged spleen may occur due to increased red blood cells distraction
- Formation of blood cells outside of the bone marrow, repeated blood transfusions or iron overload.
Affected individuals will requires frequent blood transfusions lifelong and few will live beyond their early thirties.
CAN THE CONDITION BE TREATED?
Beta thalassemia major can be treated by blood marrow transplantation from HLA-identical donor. After bone marrow transplantation, their body will be able to produce healthy blood cells.
However, unless there is a 100 percent match between the patient and the donor, there is a chance that the bone marrow will be rejected following transplantation. Efficacy of transplantation depending on how closely the HLA compatibility between donor & recipient.
FINDING THE RIGHT DONOR
It is virtually impossible to find the right donor outside the patient’s family. And even within an extended family, the likehood of finding a family member with the right genetics is still relatively low, unless the patient has a sibling.
Whereas an uncle or aunt may have a 6-10 percent chance of being compatible, a brother or sister might be 20 to 30 percent compatible.
To identify the chances of a family member’s HLA compatible, human leukocyte antigen (HLA) typing is carried out from a sample of the donor candidate’s blood.
In the case of a match being made, the donor’s bone marrow will be donated. If this is accepted, the patient will be cured.
If this happens, the parents may consider having a baby that is a complete HLA-match for their sick child.
SAVIOUR SIBLING PROGRAMME
Saviour siblings are children who are born through in-vitro fertilisation whose haematopoietic stem cells will be donated from blood in their umbilical cord so that a brother or sister may be saved.
A new matching technique called definitive high-resolution HLA genotyping is performed in a laboratory on fertilised embryos to ensure that only an embryo with the exact genetic sequence leads to pregnancy.
DIRECT HLA TYPING
Definitive high-resolution HLA genotyping using next-generation sequencing allows for much more accurate analysis of the human leukocyte antigen gene than the conventional method.
Whereas conventional HLA typing doesn’t test the gene directly rather, it looks for short tandem repeat markers throughout the HLA region.
Definitive high-resolution HLA genotyping typing looks at each of the donor’s various genetic sequences and identifies with complete accuracy if they match with those of the patient.
This accuracy is an essential component of the saviour sibling programme, since the probability is that just one in 16 embryos will provide a compatible genetic match for the sick child.
Identifying with certainty which embryo is suitable is therefore necessary before it is implanted into the mother’s womb.
In conventional HLA, 5 to 10 cells from an embryo containing on average 200 cells are removed each time a test is performed. After multiple tests, the cells in the embryo will be significantly reduced, leaving it less viable after transplantation. This means multiple biopsies is performed for multiple test that a suitable match may not result in pregnancy and the opportunity is wasted.
In contrast, direct HLA enables multiple DNA copies to be created from a single biopsy, and these copies can then be used for a wide range of tests without harming the embryo.
HOW DO STEM CELLS CURE A SICK CHILD?
Following the sibling’s birth, stem cell-rich cord blood is harvested immediately. These stem cells will then be transplanted into the patient with beta thalassemia major.
Stem cells have the potential to develop into many different types of cells throughout the body and also serve as a means to repair defects.
Cord blood contains predominantly hematopoietic stem cells that have the potential to generate blood cells and cells of the immune system, Cord blood stem cells are always a perfect match for the child and are less likely to developing graft versus host disease after transplant than stem cells harvested from other sources.
For Alpha’s savious sibling programme, stem cells are harvested by CryoCord, a Malaysian stem cell bank.