A cohort of 106 patients included in the French National Registry for Thalassemia were genotyped for 5 genetic modifiers of severity: i) β-thalassemia mutations; (ii) the XmnI SNP; (iii) the -3.7 kb α-thal deletion; (iv) the tag-SNP rs 11886868 in BCL11A exon 2; and (v) the tag-SNP rs9399137 in the HBSB1L-cMYB inter-region.