Molecular basis and hematological characterization of Hb H disease in southeast Asia.

We molecularly characterized sixty-seven cases of Hb H disease by the polymerase chain reaction. The strategy depends on amplifying the alpha-thalassemia-1 (alpha-thal-1) gene by primers flanking the breakpoint and sequence differences of the 3' end of the alpha-globin gene and the nonhomologous elements I, II, and III among different types of alpha-thala-2. In the 67 cases studied, all involved alpha-thal-1 of the Southeast Asia type (SEA) in combination with deletional or nondeletional alpha-thal-2. Thirty-two cases were of the deletion form and 35 cases were of the nondeletion form. In 32 cases of the deletion form, 29 cases were rightward deletion (-alpha 3.7), and three cases were leftward deletion (-alpha 4.2). We found that all of the nondeletion forms were alpha-thal-1 of SEA type with Hb CS. After the subtyping of Hb H with -alpha 3.7, 26 out of 29 were type I deletion and 3 out of 29 were type II deletion. Comparisons of clinical data of deletion forms and the nondeletion form showed that there were earlier occurrence of anemic symptoms and a larger erythrocyte volume in the nondeletion form group (P < 0.005).