Fetuses with homozygous
alpha-thalassemia 1, in which the deletion of all four
alpha-globin genes results in the absence of any
alpha-globin chains, are severely anemic with clinical features of
hydrops fetalis. Definitive diagnosis of
alpha-thalassemia 1 carriers is difficult since there are few red cell abnormalities. Recently Chui et al. found that minute amounts of embryonic
zeta-globin chains are present in adult
hemoglobin of the Southeast Asian type of
alpha-thalassemia 1 carriers. In this study, we screened 521 cord bloods for
alpha-thalassemia 1.
Hemoglobin analysis, including quantitation of
Hb Bart's, was performed using the automated HPLC,
alpha-thalassemia short program (VARIANT, Bio-Rad, Hercules, CA). Of these, 200 cord blood samples in which
Hb Bart's was demonstrated were tested for the presence of
zeta-globin chains by ELISA using labeled anti-zeta
monoclonal antibody.
Zeta-globin ranged between 0.21 and 0.83% in 19 specimens carrying
alpha-thalassemia 1 gene. In the remaining 90 out of 109 specimens in which
Hb Bart's was greater than 1.2%,
zeta-globin was less than 0.17%.
DNA analysis revealed the presence of normal alpha-genotype and other types of
alpha-thalassemia including
alpha-thalassemia 2 and
Hb Constant Spring. One false positive was found in which the
zeta-globin was 0.25% by ELISA but in which PCR indicated an
alpha-thalassemia 2 heterozygote. Ninety-one samples with
Hb Bart's of less than 1.2% by HPLC are most likely normal with a
zeta-globin range between 0 and 0.14%. This study also showed that the frequency of
alpha-thalassemia 1 in Bangkok is 3.65%.