Preimplantation genetic diagnosis, an alternative to conventional prenatal diagnosis of the hemoglobinopathies

Outcome of premarital genetic counseling for couples at risk of hemoglobinopathies in Kingdom of Bahrain

OBJECTIVES

Hemoglobinopathies are the commonest inherited blood disorders and form a serious burden worldwide, affecting communities, patient quality of life and healthcare resources. The Kingdom of Bahrain has issued a law obligating couples to undergo premarital screening to detect those at risk of having children affected with these disorders. The aim of this study was to analyze the marital decisions of couples at risk for hemoglobinopathies and follow up the outcomes.

METHODS

A retrospective study was conducted on couples at risk for hemoglobinopathies identified during the premarital screening program at local health centers in the Kingdom of Bahrain and referred to the genetics department in the Salmaniya Medical Complex for genetic counselling in 2018-2020.

RESULTS

A total of 189 couples were found to be at risk for hemoglobinopathies, of whom 159 completed the survey. Of these, 107 (67%) decided to proceed with their marriage and 26 couples achieved pregnancy. Out of 24 at-risk pregnancies with known outcome, 83.3% were spontaneous whereas only 16.7% underwent in-vitro fertilization (IVF) with preimplantation genetic diagnosis (PGD). Eight out of 20 infants born to couples after spontaneous conception were affected. A positive attitude toward IVF with PGD was held by 60% of at-risk couples.

CONCLUSIONS

Despite undergoing premarital screening and genetic counselling, a large percentage of at-risk couples proceeded with their marriage. Most of them justified their decision due to the availability of advanced methods that aid in the prevention of having an affected child. However, the cost of such intervention was a major barrier for the majority of couples.

Hemoglobinopathies and preimplantation diagnostics

Hemoglobinopathies constitute some of the most common inherited disorders worldwide. Manifestations are very severe, patient management is difficult and treatment is not easily accessible. Preimplantation genetic testing for monogenic disorders (PGT-M) is a valuable reproductive option for hemoglobinopathy carrier-couples as it precludes the initiation of an affected pregnancy. PGT-M is performed on embryos generated by assisted reproductive technologies and only those found to be free of the monogenic disorder are transferred to the uterus. PGT-M has been applied for 30 years now and β-thalassemia is one of the most common indications. PGT may also be applied for human leukocyte antigen typing to identify embryos that are unaffected and also compatible with an affected sibling in need of hemopoietic stem cell transplantation. PGT-M protocols have evolved from PCR amplification-based, where a small number of loci were analysed, to whole genome amplification-based, the latter increasing diagnostic accuracy, enabling the development of more generic strategies and facilitating multiple diagnoses in one embryo. Currently, numerous PGT-M cycles are performed for the simultaneous diagnosis of hemoglobinopathies and screening for chromosomal abnormalities in the embryo in an attempt to further improve success rates and increase deliveries of unaffected babies.

Ethical considerations of preconception and prenatal gene modification in the embryo and fetus

The National Academies of Sciences and Medicine 2020 consensus statement advocates the reinstatement of research in preconception heritable human genome editing (HHGE), despite the ethical concerns that have been voiced about interventions in the germline, and outlines criteria for its eventual clinical application to address monogenic disorders. However, the statement does not give adequate consideration to alternative technologies. Importantly, it omits comparison to fetal gene therapy (FGT), which involves gene modification applied prenatally to the developing fetus and which is better researched and less ethically contentious. While both technologies are applicable to the same monogenic diseases causing significant prenatal or early childhood morbidity, the benefits and risks of HHGE are distinct from FGT though there are important overlaps. FGT has the current advantage of a wealth of robust preclinical data, while HHGE is nascent technology and its feasibility for specific diseases still requires scientific proof. The ethical concerns surrounding each are unique and deserving of further discussion, as there are compelling arguments supporting research and eventual clinical translation of both technologies. In this Opinion, we consider HHGE and FGT through technical and ethical lenses, applying common ethical principles to provide a sense of their feasibility and acceptability. Currently, FGT is in a more advanced position for clinical translation and may be less ethically contentious than HHGE, so it deserves to be considered as an alternative therapy in further discussions on HHGE implementation.

Thalassemia 2016: Modern medicine battles an ancient disease

Thalassemia was first clinically described nearly a century ago and treatment of this widespread genetic disease has greatly advanced during this period. DNA-based diagnosis elucidated the molecular basis of the disease and clarified the variable clinical picture. It also paved the way for modern methods of carrier identification and prevention via DNA-based prenatal diagnosis. Every aspect of supportive care, including safer blood supply, more regular transfusions, specific monitoring of iron overload, parenteral and oral chelation, and other therapies, has prolonged life and improved the quality of life of these patients. Significant advances have also been made in allogenic bone marrow transplantation, the only curative therapy. Recently, there has been a rejuvenated interest in studying thalassemia at the basic science level, leading to the discovery of previously unknown mechanisms leading to anemia and enabling the development of novel therapies. These will potentially improve the treatment of, and possibly cure the disease. Pathways involving activin receptors, heat shock proteins, JAK2 inhibitors and macrophage targeted therapy, among others, are being studied or are currently in clinical trials for treating thalassemia. Novel types of genetic therapies are in use or under investigation. In addition to the challenges of treating each individual patient, the longer survival of thalassemia patients has raised considerations regarding worldwide control of thalassemia, since prevention is not universally implemented. This review will trace a number of the original medical milestones of thalassemia diagnosis and treatment, as well as some of the most recent developments which may lead to innovative therapeutic modalities.