We have estimated the incidence and molecular basis of alpha-thalassemia in a Portuguese population, mostly from the Greater Lisbon area. In a group of 100 consecutive cord blood samples, the gene frequency of the rightward deletion (-alpha(3.7)) was 0.035, and the leftward deletion (-alpha(4.2)) was 0.015. In this group, we have also found four heterozygotes for the trip a alpha-globin gene rearrangement (alpha alpha alpha(anti 3.7.), gene frequency 0.020). We have characterized the subtypes of -alpha(3.7) and alpha alpha alpha(anti 3.7) acta rearrangements. On the whole, these results give an incidence of 10% for deletional alpha-thalassemia carriers in the studied Portuguese population. In a group of 342 subjects presenting beta-thalassemia, or Hb S trait, beta-thalassemia major sickle cell disease or low red blood cell indices, the -alpha(3.7), -alpha(4.2), --(SEA), --(MED), (alpha alpha)(MM), and alpha alpha alpha(anti 3.7) haplotypes were found in different combinations. Only one nondeletional alpha-thalassemia determinant (a 5 nucleotide deletion in the alpha 2-globin gene in the second intervening sequence donor site) was detected, which might suggest a low incidence of these defects in the Portuguese population.
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