Preimplantation diagnosis for β-thalassemia combined with HLA matching: first “savior sibling” is born after embryo selection in Brazil

Abstract

β-Thalassemia is a common hereditary hemoglobinopathy disorder that affects many organs and represents the most common monogenetic disorder worldwide [8, 11]. Diverse phenotypes exist within the β-thalassemia syndromes, ranging from the β-thalassemia minor to the β-thalassemia major [3]. β-Thalassemia major is characterized by reduced synthesis of the hemoglobin subunit beta (hemoglobin beta chain) that results in severe anemia and hepatosplenomegaly [3, 11]. Affected children require regular blood transfusions to sustain life and, without treatment, have shortened life expectancy [14]. Treatment with a regular transfusion program and chelation therapy allows for normal growth and development and extends life expectancy into the third to fifth decade [1]. Bone marrow transplantation (BMT) remains the only definitive cure currently available for patients with β-thalassemia [3]. The success of haematopoietic stem cell (HSC) transplantation will depend on the ability of the human leukocyte antigen (HLA) types of the donor and recipient to match. When the search for compatible donors in bone marrow living donor banks and databases is exhausted, the only way to save the life of a child may be to use preimplantation genetic diagnostic (PGD) to facilitate the birth of a child who can be a matching tissue donor, the so called “savior siblings” [13]. Currently, the selection of a compatible sibling to assist a transplant is an acceptable application of PGD, through HLA haplotyping. The ESHRE PGD consortium reported that in the last decade there were 225 cycles of HLA typing along with exclusion of a specific disorder. The majority (75 %) were for β-haemoglobinopathy [4]. Other indications include Fanconi anaemia, Gaucher disease, adrenoleukodystrophy and osteopetrosis. According to the ESHRE PGD Consortium “when all other clinical options have been exhausted, PGD is acceptable for couples who already have a child affected with a malignant disorder or a genetic disorder, if the affected child is likely to be cured or life expectancy is substantially prolonged by stem cell transplantation with cord blood from a HLA-matched sibling” [5]. This article presents the first Brazilian clinical experience demonstrating feasibility of combined PGD and HLA matching for β-thalassemia major, designed to preselect for transfer only those unaffected embryos that are HLA antigen compatible with a sibling needing cord blood transplantation.