In order to determine the contribution of α-thalassemia to microcytosis and hypochromia, 339 adult outpatients seen at Unicamp University Hospital (with the exception of the Clinical Hematology outpatient clinics), who showed normal hemoglobin (Hb) levels and reduced mean corpuscular volume and mean corpuscular hemoglobin, were analyzed. Ninety-eight were Blacks (28.9%) and 241 were Caucasians (71.1%). In all cases, Hb A2 and F levels were either normal or low. The most common deletional and nondeletional forms of α-thalassemia [-α3.7, -α4.2, -MED, -(α)20.5, αHphIα, αNcolα, ααNcoI and αTSAUDI] were investigated by PCR and restriction enzyme analyses. A total of 169 individuals (49.9%) presented α-thalassemia: 145 (42.8%) were heterozygous for the -α3.7 deletion (-α3.7/αα) and 18 (5.3%) homozygous (-α3.7/-α3.7), 5 (1.5%) were heterozygous for the nondeletional form αHPhlα/αα, and 1 (0.3%) was a -MED carrier (-MED/αα). Among the Blacks, 56 (57.1%) showed the -α3.7/ αα genotype, whereas 12 (12.2%) were -α3.7/-α3.7 and I (1.0%) was an αHPhlα carrier; among the Caucasians, 89 (36.9%) were -α3.7/αα, 6 (2.5%) had the -α3.7/-α3.7 genotype, 4 (1.7%) presented the nondeletional form (αHPhlα/αα), and 1 (0.4%) was a -MED carrier. These results demonstrate that α-thalassemia, mainly through the -α3.7 deletion, is an important cause of microcytosis and hypochromia in individuals without anemia. These data are of clinical relevance since these hematological alterations are often interpreted as indicators of iron deficiency.346759762Weatherall, D.J., Clegg, J.G., (1981) The Thalassaemia Syndromes. 3rd Edn., , Blackwell Scientific Publications, OxfordBunn, H.F., Forget, B.G., (1986) Hemoglobin: Molecular, Genetics and Clinical Aspects, , W.B. Saunders, PhiladelphiaHiggs, D.R., Vickers, M.A., Wilkie, A.O.M., Pretorius, I.M., Jarman, A.P., Weatherall, D.J., A review of the molecular genetics of the human α-globin gene cluster (1989) Blood, 73, pp. 1081-1104Kazazian H., Jr., The thalassemia syndromes: Molecular basis and prenatal diagnosis in 1990 (1990) Seminars in Hematology, 27, pp. 209-228Harteveld, K.L., Losekoot, M., Ajgam, H., Van Der Wielen, M., Giordano, P.C., Bernini, L.F., α-Thalassaemia in the Netherlands: A heterogeneous spectrum of both deletions and point mutations (1997) Human Genetics, 100, pp. 465-471Higgs, D.R., α-Thalassaemia (1993) Baillieres Clinical Haematology, 6, pp. 117-150Kattamis, A.C., Camaschella, C., Sivera, P., Surrey, S., Fortina, P., Human α-thalassemia syndromes: Detection of molecular defects (1996) American Journal of Hematology, 53, pp. 81-91Bianco, I., Cappabianca, M.P., Foglietta, E., Lerone, M., Deidda, G., Morlupi, L., Grisanti, P., Graziani, B., Silent thalassemias: Genotypes and phenotypes (1997) Haematologica, 82, pp. 269-280Galanello, R., Sollaino, C., Paglietti, E., Barella, S., Perra, C., Doneddu, I., Pirroni, M.G., Cao, A., α-Thalassemia carrier identification by DNA analysis in the screening for thalassemia (1998) American Journal of Hematology, 59, pp. 273-278Sonati, M.F., Costa, F.F., Hemoglobin Bart's in a Brazilian black population (1990) Brazilian Journal of Medical and Biological Research, 23, pp. 395-396Sonati, M.F., Farah, S.B., Ramalho, A.S., Costa, F.F., High prevalence of α-thalassemia in a Black population of Brazil (1991) Hemoglobin, 15, pp. 309-311Zago, M.A., Costa, F.F., Bottura, C., Hemoglobin H disease in three Brazilian families (1984) Revista Brasileira de Genética, 7, pp. 137-147Wenning, M.R.S.C., Kimura, E.M., Costa, F.F., Saad, S.T.O., Gervásio, S.A., De Jorge, S.B., Borges, E., Sonati, M.F., α-Globin genes: Thalassemic and structural alterations in a Brazilian population (2000) Brazilian Journal of Medical and Biological Research, 33, pp. 1041-1045Dodé, C., Krishnamoorthy, R., Lamb, J., Rochette, J., Rapid analysis of -α3.7 thalassaemia and αααanti 3.7 triplication by enzymatic amplification analysis (1993) British Journal of Haematology, 82, pp. 105-111Bowden, D.K., Vickers, M.A., Higgs, D.R., A PCR-based strategy to detect the common severe determinants of a thalassaemia (1992) British Journal of Haematology, 81, pp. 104-108Oron-Karni, V., Filon, D., Oppenheim, A., Rund, D., Rapid detection of the common Mediterranean α-globin deletions/rearrangements using PCR (1998) American Journal of Hematology, 58, pp. 306-310Hall, G.W., Thein, S.L., Newland, C.A., Chisholm, J.T.S., Kanavakis, E., Kattamis, C., Higgs, D.R., A base substitution (T→C) in codon 29 of the α2-globin gene causes α thalassemia (1993) British Journal of Haematology, 85, pp. 546-552Pearson, H.A., Ehrenkranz, R.A., Rinder, H.M., Hemosiderosis in a normal child secondary to oral iron medication (2000) Pediatrics, 105, pp. 429-43