Birth of a savior sibling after preimplantation genetic testing for beta-thalassemia, HLA haplotyping and aneuploidy screening

Abstract

Aim:  To undertake preimplantation genetic testing (PGT) for a couple where both partners are carriers of the c.126_129delCTTT variation in the HBB gene and have a daughter affected with beta-thalassemia major. This is with the hope of selecting thalassemia unaffected, human leukocyte antigen (HLA) matched, chromosomally normal embryos for transfer to get a saviour sibling, to help cure their daughter with related, HLA matched hematopoietic stem cell transplantation in the near future.

Methods: Pre-test genetic counselling and pre-PGT for monogenic disorders (PGT-M) study was done on the family by combined direct and indirect approach on the HBB gene and indirect genetic study of the HLA region by fluorescent polymerase chain reaction (PCR). Couple karyotyping was done to rule out balanced chromosomal rearrangements. The couple underwent 3 in vitro fertilization (IVF) cycles from June 2019 to November 2019 to collect adequate embryos which were biopsied at the day 5/6 blastocyst stage prior to vitrification. The biopsied cells were tubed and frozen. Genetic analysis was carried out on 14 embryo biopsies starting with whole genome amplification. Direct detection of c.126_129delCTTT polymorphism was carried out by PCR amplification and genotyping. Indirect studies included PCR amplification of polymorphic markers linked to HBB gene, and HLA region. Fragment analysis of the PCR products was done by capillary electrophoresis. The unaffected embryos were further subjected to 24 chromosomes aneuploidy screening by Next Generation Sequencing (NGS).

Results: Of the 14 embryo biopsies tested, one was uninformative, while 10 were unaffected with beta-thalassemia. Of these, six were chromosomally normal or euploid, though only one was HLA matched with the affected child. Though this embryo was unaffected, it was heterozygous for the c.126_129delCTTT polymorphism. A healthy baby was born and the umbillical cord blood stem cells have been stored for later use with bone marrow stem cells after the child is two years old.

Conclusion: This HLA matched saviour sib will help to cure the couple’s elder child suffering from beta-thalassemia major, with tailored hematopoietic stem cells. This is the first such report from Mumbai, and 2^nd in India. Awareness needs to be spread for the benefit of others.