Molecular spectrum of beta-thalassemia in the Mexican population.

Beta-thalassemia (beta-thal) is present in 59% and 75% of patients with abnormal hemoglobin disorders in northwestern and central Mexico, respectively. In our Research Center, up until 1997, we reported the presence of 13 beta-thal alleles in 26 unrelated chromosomes (-28A>C; -87C>T; MET1VAL; IVS1, G>A, +1; IVS1, G>A, +5; IVS1, G>C, +5; IVS1, G>A, +110; IVS2, C>G, +745; GLU6FS; VAL11FS; GLN39TER; HBD/HBB 104 kb del; and HBD87/HBB116 fusion). Since then, 57 more beta-thal chromosomes have been identified by the amplification-refractory mutation system (ARMS) and DNA sequencing from 54 individuals with beta-thalassemia (seven compound heterozygotes, three with two beta-thal alleles, three with beta-thal and HbS, and one with beta-thal and HbD; and 47 beta-thal heterozygotes). Nine of the previously observed alleles were found, together with three new alleles: IVS2, G>A, +1; LYS17TER; and 4-bp del, 41/42CTTT. Moreover, a novel mutation was observed, HIS77FS, bringing to a total of 17 beta-thal alleles identified in our population. Six alleles constitute 78.3% of the observed alleles: five Mediterranean alleles (GLN39TER; IVS1, G>A, +1; IVS1, G>A, +110; HBD/HBB 104 kb del; and IVS1, G>A, +5) and one common in the Kurdish population (-28A>C). We note especially the presence in these families of -28A>C and VAL11FS, both of which have previously been considered private alleles. The observed spectrum of mutations is characteristic of populations with low frequencies of thalassemias. Because thalassemia is not a rare disease in Mexico, we emphasize its necessary consideration in the differential diagnosis of microcytic hypochromic anemia.