International Thalassaemia Day 2022: The genetic perspective of Thalassemia

FPJ Web DeskUpdated:Saturday, May 07, 2022, 11:48 PM IST
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International Thalassaemia Day 2022: The genetic perspective of Thalassemia | Photo: Representative Image

Five percent of the human population is carrier of some form of disorder of Hemoglobin (Hb) (Hemoglobinopathy) affecting its oxygen carrying capacity in blood, as per to WHO. Prevalence rate for Thalassemia (a type of hemoglobinopathy) mutations have been reported to be as high as 17% by studies from Indian subcontinent. Thalassemia and Sickle cell disease are the most common of Hemoglobinopathies and are inherited in an Autosomal recessive manner, meaning that if both partners are carrier of a mutation in the Hb gene, then the risk of having an child affected with Thalassemia major is about 25%. This risk becomes even more significant in view of the high prevalence of Hb gene mutation carrier status in general population (tribal belts, Sindhis, Parsis, Gujratis and specific pockets in south India), marriages within closed communities and consanguinity (marriages within relation)

Treatment of Thalassemia major is lifelong and includes regular blood transfusions, chelation medicines to tackle the issue of increasing iron content in body, managing any complications such as infections, endocrine – resulting hormonal imbalances. While Hematopoietic stem cell transplantation (HSCT) is the only curative therapy available currently for patients with β-thalassemia major, it is limited by feasibility, cost and availability of suitable matched donor. HSCT is also associated with potential risk of immune-mediated rejection and graft-versus-host disease (GVHD) in few cases. Gene therapy trails have provided a new impetus in this field.

Routine screening for Hemoglobinopathies is done by Hb electrophoresis of HPLC (high performance liquid chromatography). This helps identify the particular disorder and institute prompt treatment and follow up. However such HPLC has major have limitations as all Hb variants may not be detected by HPLC and when screening the neonates or doing prenatal testing (specific testing done during pregnancy to know if the fetus is affected) as the pattern of functioning Hb gradually shifts from fetal type to adult type by around one year of age. Also blood transfusions may influence the HPLC results.  Herein comes the importance of Molecular genetic testing. Hundreds of Hemoglobinopathies causing alterations in the HBB gene have been reported, curated and catalogued in various databases. It must be noted that about 5 common mutations in the HBB gene account for over 90% cases of Thalassemia. Making them the first line of mutations to be tested if suspecting Thalassemia. If these are negative then we proceed with the HBB gene sequencing.

Dr. AnupKumar Rawool, Associate Director, Clinical Genomics, SRL Diagnostics said, "Living with Thalessemia is not an easy lifestyle and if not diagnosed correctly or at the right time, can lead to other health problems. We know that Thalessemia and Beta Thalessemia is prevalent in India and there is research underway for better cure, treatment and therapy of the illness. While there are other forms of treatment available, the newest treatment now making waves all over the world is Gene Therapy. We now have studies to prove that Gene Therapy is a viable cure for beta thalessemia. It has therapeutic potential and we are excited to have with us this indispenasable expertise that is is key to good health for countless patients in our country.

"Timely diagnosis of genetic disorders with appropriate Molecular genetic tests provides an optimum window for offering prenatal diagnosis and decision making for the family. It is recommended that the person with thalassemia or any Hemoglobinopathy undergo HBB sequencing test to identify the disease causing alterations in the HBB gene. Once these are identified and confirmed then diagnostic testing during pregnancy can be offered by either Chorionic villi sampling between 11-13 weeks or amniocentesis after 16 completed weeks of gestation, leaving ample time for the molecular genetic lab to perform and report the test and for the clinician, medical geneticist and the family for appropriate pre and post test genetic consultation and decision making accordingly. It is advisable that Planning for prenatal testing to be done prior to pregnancy. Advances in molecular testing techniques also provide option for testing embryos on day 5 by pre-implantation genetic diagnosis (PGD) if availing an option of IVF/ART. So prior screening of embryo can be done for any known genetic disorder in the family. However PGD services are available at limited centres. A prior Genetic consultation with a Medical Geneticist for the families in such situation is strongly recommended to smoothen the entire process.

Timely diagnosis of genetic disorders with appropriate Molecular genetic tests provides an optimum window for offering prenatal diagnosis and decision making for the family. It is recommended that the person with thalassemia or any Hemoglobinopathy undergo HBB sequencing test to identify the disease causing alterations in the HBB gene. Once these are identified and confirmed then diagnostic testing during pregnancy can be offered by either Chorionic villi sampling between 11-13 weeks or amniocentesis after 16 completed weeks of gestation, leaving ample time for the molecular genetic lab to perform and report the test and for the clinician, medical geneticist and the family for appropriate pre and post test genetic consultation and decision making accordingly. It is advisable that Planning for prenatal testing to be done prior to pregnancy. Advances in molecular testing techniques also provide option for testing embryos on day 5 by pre-implantation genetic diagnosis (PGD) if availing an option of IVF/ART. So prior screening of embryo can be done for any known genetic disorder in the family. However PGD services are available at limited centres. A prior Genetic consultation with a Medical Geneticist for the families in such situation is strongly recommended to smoothen the entire process.

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