In order to determine the prevalence and molecular basis of alpha-thalassemia (thal) among Filipinos, a total of 2954 Filipinos in Taiwan were enrolled in this study. A complete blood count was done for every subject. Those with microcytosis (MCV less than 82.5 fl) were studied with hemoglobin (Hb) high-performance liquid chromatography to determine the levels of Hb A2 and Hb F, and with an enzyme immunoassay to determine plasma ferritin levels. Those who had microcytosis and normal or low levels of Hb A2 and Hb F were further studied with molecular methods for alpha-globin gene mutations. We used Southern blot hybridization and/or the polymerase chain reaction to detect Southeast Asian deletion, Filipino deletion, rightward and leftward single alpha-globin gene deletions, and Hb Constant Spring and Hb Quong Sze. Specific amplification and direct DNA sequencing of the alpha2- and alpha1-globin genes were carried out in apparent alpha-thal carriers without any of the above-mentioned mutations. Our results showed that in Filipinos the prevalence of alpha-thal 1 was 5% (147 carriers) and that of alpha-thal 2 was 1.7% (49 carriers); two had Hb H disease. Among the alpha-thal 1 carriers, 89 had the Southeast Asian deletion and 58 had the Filipino deletion. Among the alpha-thal 2 carriers, 48 had a rightward deletion and one had a leftward deletion. None had Hb Constant Spring or Hb Quong Sze. Specific amplification and DNA sequencing in five apparent alpha-thal carriers did not reveal mutations in the 2-kb region spanning the alpha2- and alpha1-globin genes. The molecular defects of alpha-thal in Filipinos were different from those in the neighboring ethnic groups. Elucidation of the alpha-thal mutations in Filipinos is useful in the genetic counseling and prenatal diagnosis of this common disease.
Beta-thalassemia (thal) is a common single-gene disease worldwide. However, the prevalence of beta-thal and the spectrum of beta-globin gene mutations in Filipinos remain unclear. This study sought to answer these two questions. A total of 2954 apparently healthy Filipinos in Taiwan were recruited for a prevalence study. A complete blood count was done in every subject. Those with microcytosis were studied with hemoglobin (Hb) high-performance liquid chromatography to determine the levels of Hb A2 and Hb F. Twenty-seven subjects had elevated levels of Hb A2 (>4.0%). These 27 suspected beta-thal carriers and another 16 beta-thal major patients who were being treated in the Philippines were studied to determine the spectrum of beta-globin gene mutations. Gap-PCR was used to detect the Filipino deletion of beta-thal, and direct sequencing was used to detect point or small mutations in the beta-globin gene. All of the 27 suspected beta-thal carriers had one mutation in the beta-globin gene, resulting in an overall prevalence of 0.9%. The spectrum of beta-thal mutations was similar in the carrier and patient groups. Analysis of the pooled identified seven different mutations in the study population. The Filipino deletion was the most common mutation, accounting for 45.8% (27/59) of the alleles, followed by codon 67 (-TG) (16 alleles), and Hb E (11 alleles). These three mutations accounted for 92% of the Filipino beta-thal alleles. Elucidation of the beta-thal mutations in Filipinos is useful for the genetic counseling and prenatal diagnosis of this disease.
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