GSTM1 and thalassemia: Table 4 demonstrates the number of risk alleles among thalassemia or Hb E-related blood donors. From all blood donors, there are 17 alleles (from 13 blood donors) that can cause the severe thalassemia in the offspring (risk allele frequency = 3.7%). Among 17 risk alleles, Hb E allele (βE) is the most common form of all risk alleles (–/, β0/+ and βE), 12/17 (70.6%), followed by α-thalassemia 1 allele (–/), 4/17 (23.5%), and β-thalassemia allele (β0/+), 1/17 (5.9%).