Molecular basis of α-thalassemia

α-Thalassemia is an inherited, autosomal recessive, disorder characterized by a microcytic hypochromic anemia. It is one of the most common monogenic gene disorders in the world population. The clinical severity varies from almost asymptomatic, to mild microcytic hypochromic, and to a lethal hemolytic condition, called Hb Bart's Hydrops Foetalis Syndrome. The molecular basis are usually deletions and less frequently, point mutations affecting the expression of one or more of the duplicated α-genes. The clinical variation and increase in disease severity is directly related to the decreased expression of one, two, three or four copies of the α-globin genes. Deletions and point mutations in the α-globin genes and their regulatory elements have been studied extensively in carriers and patients and these studies have given insight into the α-globin genes are regulated. By looking at naturally occurring deletions and point mutations, our knowledge of globin-gene regulation and expression will continue to increase and will lead to new targets of therapy.

α0-Thalassemia Due to a 90.7 kb Deletion (- -NFLD)

We report an α⁰-thalassemia (α⁰-thal) trait in Newfoundlanders caused by a novel 90.7 kb deletion. The deletion, designated the Newfoundland deletion (- -^NFLD), removes both the HBA2 and HBA1 genes, while leaving the HBZ gene intact. The 5' deletion endpoint is within the HBAP1 pseudogene, approximately 3.7 kb upstream of the HBA2 gene. The 3' deletion endpoint is approximately 82.5 kb downstream of the HBA1 gene, within the second intervening sequence (IVS-II) of the FAM234A gene. This is the second α⁰-thal deletion reported in Newfoundland families of northern European descent.

Complex Interaction of Hb Q-Thailand with α0- and β0-Thalassemia in a Chinese Family

Hb Q-Thailand [α74(EF3)Asp→His (α1); HBA1: c.223 G>C] is an abnormal hemoglobin (Hb), variant found mainly in China and Southeast Asian countries. The association of the α^Q-Thailand allele with other globin gene disorders has important implications in diagnosis. Here, we report a hitherto undescribed condition of patients with a double heterozygosity for Hb Q-Thailand with α⁰-thalassemia (α⁰-thal) and in combination with β⁰-thalassemia (β⁰-thal) in a Chinese family. Our study will provide some clinical manifestations, laboratory diagnosis and genetic counseling for complex hemoglobinopathies.

An Alu element-mediated 28.5 kb α-thalassemia deletion found in a Chinese family

Over 95.0% of the α-thalassemia (α-thal) cases in southern China are caused by large deletions involving the α-globin gene. Here, we describe the molecular characterization of a novel 28.5 kb deletion that eliminated one of the duplicated α-globin genes in a Chinese family. The deletion breakpoint fragment involved Alu repeat sequences, suggesting a homologous recombination event. Phenotypic analysis on the heterozygous carrier of this deletion revealed that it leads to a very mild phenotype. Because of a 25.0% risk of Hb H (β4) disease in the offspring when in combination with another α(0)-thal allele, we should not ignore screening the deletion in prenatal diagnosis in order to decrease reproductive risk.