Prevalence study and molecular characterization of alpha-thalassemia in Filipinos

In order to determine the prevalence and molecular basis of cr-thalassemia (thal) among Filipinos, a total of 2954 Filipinos in Taiwan were enrolled i n this study. A complete blood count was done for every subject. These with microcytosis (MCV less than 82.5 fl) were studied with hemoglobin (Hb) hig h-performance liquid chromatography to determine the levels of Hb A2 and Hb F, and with an enzyme immunoassay to determine plasma ferritin levels. Tho se who had microcytosis and normal or low levels of Hb A2 and Hb F were fur ther studied with molecular methods for alpha-globin gene mutations. We use d Southern blot hybridization and/or the polymerase chain reaction to detec t Southeast Asian deletion, Filipino deletion, rightward and leftward singl e alpha-globin gene deletions, and Hb Constant Spring and Hb Quong Sze. Spe cific amplification and direct DNA sequencing of the alpha 2- and alpha 1-g lobin genes were carried out in apparent alpha-thal carriers without any of the above-mentioned mutations. Our results showed that in Filipinos the pr evalence of alpha-thal 1 was 5% (147 carriers) and that of alpha-thal 2 was 1.7% (49 carriers); two had Hb II disease. Among the alpha-thal 1 carriers , 89 had the Southeast Asian deletion and 58 had the Filipino deletion. Amo ng the alpha-thal 2 carriers, 48 had a rightward deletion and one had a lef tward deletion. None had Hb Constant Spring or Hb Quong Sze. Specific ampli fication and DNA sequencing in five apparent alpha-thal carriers did not re veal mutations in the 2-kb region spanning the alpha 2- and alpha 1-globin genes. The molecular defects of alpha-thal in Filipinos were different from those in the neighboring ethnic groups. Elucidation of the alpha-thal muta tions in Filipinos is useful in the genetic counseling and prenatal diagnos is of this common disease.