Chapter 7: Genetic Disorders of Haemoglobin

Genetic Disorders of Haemoglobin begins by detailing the developmental transition of hemoglobin synthesis from embryonic and fetal stages to adulthood, noting the critical switch from fetal hemoglobin to adult hemoglobin which occurs several months after birth. The genetic architecture is centered on clusters located on chromosomes 11 and 16, where precise regulation ensures a balance between alpha and beta globin chains. The primary focus shifts to the thalassaemias, characterized by a deficit in globin chain synthesis. Alpha-thalassaemia is frequently caused by gene deletions, ranging from a silent carrier state to the fatal hydrops fetalis or the moderate anaemia seen in Haemoglobin H disease. Beta-thalassaemia typically results from point mutations, leading to clinical spectrums from the asymptomatic minor trait to the severe, transfusion-dependent thalassaemia major. These conditions often lead to complications like ineffective erythropoiesis, chronic haemolysis, and iron overload requiring lifelong chelation therapy. Furthermore, the chapter examines structural variants, most notably sickle cell disease, caused by a specific amino acid substitution that results in haemoglobin polymerization and red cell deformation under low oxygen levels. This leads to debilitating vaso-occlusive crises, organ infarction, and chronic haemolytic anaemia. Other common variants such as Haemoglobin C, D, and E are also discussed, often in the context of their geographical distribution and interaction with thalassaemia traits. Diagnostic methodologies, including high-performance liquid chromatography, electrophoresis, and molecular techniques like PCR, are essential for identifying these disorders. Management strategies have evolved to include regular blood transfusions, folic acid supplementation, and pharmacological interventions like hydroxycarbamide to boost fetal haemoglobin levels. Advanced curative options such as allogeneic stem cell transplantation and emerging gene therapy techniques, including CRISPR/Cas9 editing, offer hope for permanent resolution. Finally, the role of genetic counselling and prenatal diagnosis through chorionic villus sampling is emphasized to assist at-risk families in making informed reproductive decisions.