b-Thalassemia/HbE disease is clinically variable. In searching for genetic factors modifying the disease severity, patients were selected based on their disease severities, and a genome-wide association study (GWAS) was performed. Genotyping was conducted with the Illumina Human 610-Quad BeadChips array using DNAs from 618 Thai b0-thalassemia/HbE patients who were classified as 383 severe and 235 mild phenotypes by a validated scoring system. Twenty-three SNPs in three independent genes/regions were identified as being significantly associated with the disease severity. The highest association was observed with SNPs in the b-globin gene cluster (chr.11p15), and rs2071348 of the HBBP1 gene revealed the most significant association [P = 2.96 9 10(-13), odds ratio (OR) = 4.33 (95% confidence interval (CI), 2.74-6.84)]. The second was identified in the intergenic region between the HBS1L and MYB genes (chr.6q23), among which rs9376092 was the most significant [P = 2.36 9 10(-10), OR = 3.07 (95% CI, 2.16-4.38)]. The third region was located in the BCL11A gene (chr.2p16.1), and rs766432 showed the most significant association [P = 5.87 9 10-10, OR = 3.06 (95% CI, 2.15-4.37)]. All three loci were replicated in an independent cohort of 174 Indonesian patients. The associations to fetal hemoglobin levels were also observed with SNPs on these three regions. Our data indicate that several genetic loci act in concert to influence HbF levels of beta(0)-thalassemia/HbE patients. This study revealed that all the three reported loci and the alpha-globin gene locus are the best and common predictors of the disease severity in beta-thalassemia.

intermediate patients show a remarkable clinical heterogeneity. We examined the phenotypic diversity of 950 b-thalassemia/Hb E patients in an attempt to construct a system for classifying disease severity. A novel scoring system based on six independent parameters, hemoglobin level, age at disease presentation, age at receiving first blood transfusion, requirement for transfusion, spleen size, and growth and development, was able to separate patients into three distinctive severity categories: mild, moderate, and severe courses. This system, therefore, can increase the accuracy of studies of genotype-phenotype interactions and facilitate decisions for appropriate patient management. Am. J. Hematol. 83:482-484, 2008. V

BackgroundPatients with Hb E/β0 thalassemia display remarkable variability in disease severity. To identify genetic modifiers influencing disease severity, we conducted a two-stage genome scan in groups of 207 mild and 305 severe unrelated patients from Thailand with Hb E/β0 thalassemia and normal α-globin genes.MethodsFirst, we estimated and compared the allele frequencies of approximately 110,000 gene-based single nucleotide polymorphisms (SNPs) in pooled DNAs from different severity groups. The 756 SNPs that showed reproducible allelic differences at P < 0.02 by pooling were selected for individual genotyping.ResultsAfter adjustment for age, gender and geographic region, logistic regression models showed 50 SNPs significantly associated with disease severity (P < 0.05) after Bonferroni adjustment for multiple testing. Forty-one SNPs in a large LD block within the β-globin gene cluster had major alleles associated with severe disease. The most significant was bthal_bg200 (odds ratio (OR) = 5.56, P = 2.6 × 10-13). Seven SNPs in two distinct LD blocks within a region centromeric to the β-globin gene cluster that contains many olfactory receptor genes were also associated with disease severity; rs3886223 had the strongest association (OR = 3.03, P = 3.7 × 10-11). Several previously unreported SNPs were also significantly associated with disease severity.ConclusionsThese results suggest that there may be an additional regulatory region centromeric to the β-globin gene cluster that affects disease severity by modulating fetal hemoglobin expression.