Hemoglobin H Disease in two Turkish Females and one Iranian Newborn

Abstract

Recent advances in molecular biology has resulted in the characterization of different forms of α-thalassemia (α-thal). Deletion, or occasionally dysfunction, of one or both α globin genes, which are located on the short arm of chromosome #16 (l), will lead to an α chain deficiency with variable alterations in red cell indices. α-Thal-2 or αα/-α results from deletion of one of the two a globin genes, i.e. either the leftward or 4.2 kb deletion involving the α₂ globin gene or the rightward or 3.7 kb deletion which involves the 3′ segment of the α₂ gene, the 5 ′ segment of the a1 gene and intergenic DNA. α-Thal-1 or αα/- results from larger deletions involving segments of DNA which contain both the α2 globin gene and (part of) the α1 globin gene. The various types are due to misalignment between two strands of DNA from two separate chromosomes during meiosis followed by an unequal crossover generating chromosomes with a single (or no) functional a globin gene or with triplicated a globin genes (2, and references quoted). Appropriate combinations of these chromosomes will lead to an α-thal-2 homozygosity (α-/α-), to Hb H disease (−/α-), to hydrops fetalis (- - / - -), and to genetic conditions such as those characterized by the presence of five (ααα/αα), four (ααα/α-) or three (ααα/−) a globin genes (2,3,4)