MOLECULAR-BASIS OF ALPHA-THALASSEMIA IN PORTUGAL

We have estimated the incidence and molecular basis of alpha-thalassem ia 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 delet ion (-alpha(4.2)) was 0.015. In this group, we have also found four he terozygotes for the trip a alpha-globin gene rearrangement (alpha alph a alpha(anti 3.7.), gene frequency 0.020). We have characterized the s ubtypes of -alpha(3.7) and alpha alpha alpha(anti 3.7) acta rearrangem ents. On the whole, these results give an incidence of 10% for deletio nal alpha-thalassemia carriers in the studied Portuguese population. I n a group of 342 subjects presenting beta-thalassemia, or Hb S trait, beta-thalassemia major sickle cell disease or low red blood cell indic es, the -alpha(3.7), -alpha(4.2), --(SEA), --(MED), (alpha alpha)(MM), and alpha alpha alpha(anti 3.7) haplotypes were found in different co mbinations. Only one nondeletional alpha-thalassemia determinant (a 5 nucleotide deletion in the alpha 2-globin gene in the second interveni ng sequence donor site) was detected, which might suggest a low incide nce of these defects in the Portuguese population.