Biochem Genet DOI 10.1007/s10528-015-9687-8 REVIEW ARTICLE

The Influence of Polymorphisms in Disease Severity in b-Thalassemia Javad Mohammdai-Asl1 • Abolfazl Ramezani2 • Fatemeh Norozi2 • Arash Alghasi2 • Ali Amin Asnafi2 Kaveh Jaseb2 • Najmaldin Saki2

•

Received: 26 May 2015 / Accepted: 24 June 2015 Ó Springer Science+Business Media New York 2015

Abstract b-Thalassemia is a genetic disorder with a continuum of mild to severe clinical manifestations and requirement of transfusion at different stages of life. The cause(s) of this variety is not clear but genetic alterations could be a potential factor. In this review, the correlation between polymorphisms and different clinical manifestations, including the need for transfusion, was investigated. Relevant articles published in pubmed database from 1982 onwards were studied and compiled. The articles all contained the keywords b-thalassemia, genetic modifiers, and mutations. Certain polymorphisms and mutations could dictate the severity of symptoms as well as their onset. A significant number of the mentioned genetic alterations appear in beta-globin gene cluster and affect gamma chain. Therefore, hemoglobin F production rate is increased and can affect thalassemia symptoms and can relieve bthalassemia symptoms. A number of polymorphisms in catalase and glutathione S transferase genes have also been shown to modify the severity of disease and response to treatment. Knowledge of these mutations and polymorphisms can provide an insight into the prognosis for individual patients, especially in young ages or before birth to take proper measures in advance and eventually ameliorate the symptoms in the long run. Keywords

b-Thalassemia  Polymorphisms  Mutations

& Najmaldin Saki [email protected] 1

Department of Medical Genetics, Ahvaz Jundishapur University of Medical Sciences, Ahvaz, Iran

2

Health Research Institute, Research Center of Thalassemia & Hemoglobinopathy, Ahvaz Jundishapur University of Medical Sciences, Ahvaz, Iran

123

Biochem Genet

Introduction Thalassemia is a widespread disease most prevalent in the Mediterranean region, Middle-East, India, and South-East Asia, cutting a swath of high mortality and morbidity in the mentioned areas (Ehteram et al. 2014). The major form of thalassemia is the most severe in which both alleles are mutant. In case the mutation totally diminishes the gene function, homozygosis results in translation of almost no amount of beta-globin chain and is shown as b0/b0. Roughly a third of thalassemia patients are b0/b0 (Dehghanifard et al. 2013). The resulting imbalance between the globin chains leads to alpha-chain accumulation in erythroid cells and subsequently to hemolytic anemia and ineffective erythropoiesis (Svasti et al. 2010). These patients depend on regular transfusions for survival, a treatment which in itself complicates their condition by iron overload and precipitation in issues such as heart and liver (Musallam et al. 2012). In normal individuals, hemoglobin F (HbF) (a2c2) is the dominant hemoglobin at birth, which is gradually decreased with increasing age and changes to adult hemoglobin (HbA) (a2b2), while in patients with thalassemia major, defective b chain gene causes decreased HbA synthesis as well as increased expression of HbF (Bauer and Orkin 2011; Sankaran and Orkin 2013). Several studies have shown that HbF expression is affected by several factors, including post-transcriptional regulatory mechanisms as well as single nucleotide polymorphisms (SNPs) in quantitative trait loci (QTLs) (Alijani et al. 2014). XmnI-Gc in b-globin locus on chromosome 11p15, HBS1L-MYB intergenic region on chromosome 6q23, and oncogene BCL11A on 2p15 chromosome can be cited as important QLTs (Garner et al. 2000; Menzel et al. 2007). Over 600 mutations have been reported in the beta-globin locus, approximately 200 of which are related to beta-thalassemia in some capacity (Hung et al. 2008; Hardison et al. 2002). Most mutations altering HbF levels happen in the promoter of Ac and Bc genes between upstream -114 and -205 and the transcription origin. There also are a number of mutations in GATA1 junction, NF-E4 and the upstream CAAT box (Dassanayake et al. 2013; Haj Khelil et al. 2011). A handful of the most prevalent mutations associated with thalassemia are listed in Table 1 along with related symptoms. In the following, we review these mutations and their correlation with beta-thalassemia symptom severity.

The HBG2-XMN1 158 polymorphism This common variation, also known as XMN1 (C[T) or rs7382144, is located on chromosome 11 in the -158 upstream of c-globin gene in its promoter region (Garner et al. 2000; Neishabury et al. 2013).This mutation is known to be a cisacting factor, and studies have reported that it up-regulates HbF production and might play a role in the onset of symptoms and transfusion need (Haj Khelil et al. 2011).

123

Biochem Genet Table 1 The common polymorphisms in b-thalassemia patients Gene

SNP

Chromosome

Allele

Effect of polymorphism

Ref.

Xmn 1-HBG2

rs7482144

11p 15.4

C/T

TT genotype associated with high HbF in TM patients

Neishabury et al. (2013), Lettre et al. (2008)

rs11886868

2p16.1

C/T

C allele is associated with elevated HbF in TM patients

Sedgewick et al. (2008), Nguyen et al. (2010)

BCL11A

rs766432

C/A

rs4671393 HBS1LMYB

rs4895441

6q23

C/T

C allele is associated with elevated HbF in TM patients

Lettre et al. (2008), Gorji et al. (2011), Pandit et al. (2008)

rs28384513 rs9399137

Col IAI

Sp1 site1997G/T

–

G/T

G allele is associated with low BMD and an increased risk of osteoporosis in TM patients

Singh et al. (2013), Kostik et al. (2013)

HBBP1

rs2071348

11

A/C

C allele is associated with higher HbF levels and a milder b-thalassemia disease phenotype

Kerdpoo et al. (2014), Giannopoulou et al. (2012)

Exon 9 CAT

rs769217

11p13

C/T

T allele is associated with decreased blood catalase activity

Casp et al. (2002), Nagy et al. (2012)

GSTM1

–

1p13.3

–

GSTT1

–

22q11.23

–

GSTT1 null genotype could be considered as a predisposing factor for b-thalassemia, myocardial siderosis, and dysfunction in patients with this disease

Hahn et al. (2010), Sclafani et al. (2013)

(AT)9 (T)5 motif

?179C?T

11

C/T

T allele is associated with increased level of HbF in b-thalassemia

Chen et al. (2010), Dabket al. Dabke et al. (2013)

G113A G5A

COL IAI collagen type I alpha 1, CAT catalase, GSTM glutathione S-transferase M1, glutathione S-transferase T1, TM thalassemia major

In her 2013 article, Neishabury showed that a G[A polymorphism in 50 HS4 palindromic sequence was highly correlated with HBG2-XMN1 C[T, elevated HbF levels as well as improved clinical symptoms (Neishabury et al. 2013).

BCL11A Polymorphisms BCL11A gene on band 2p16 encodes a C2H2-type zinc finger protein that represses the c-globin gene expression (Sedgewick et al. 2008; Fanis et al. 2014). The two major isoforms of this gene product, including xL and L, attach to the locus control

123

Biochem Genet

region (LCR) as well as an intergenic region in the b-globin gene cluster (Fanis et al. 2014). This ultimately inhibits c-globin synthesis and switching from hemoglobin F to A (Uda et al. 2008). A couple of SNPs, rs11886868 and rs766432 in BCL11A, are indicated to be associated with an up-regulation of fetal hemoglobin synthesis (Nguyen et al. 2010). The rs4671393 SNP, in the second intron of BCL11A, has also been shown to increase HbF in thalassemic patients (Stadhouders et al. 2013).

Polymorphisms in Exon-1 of HBS1L-MYB Gene MyB is a proto-oncogene playing a critical role in erythroid cell proliferation and differentiation, while also controlling HbF levels through an unknown mechanism (Fanis et al. 2014; Stadhouders et al. 2013). HBS1L-MYB intergenic polymorphism (HMIP) on 6q23.3 co-regulates the number of F-cells (Gorji et al. 2011; Wonkam et al. 2014). In addition, the SNPs rs4895441, rs28384513, and rs9399137 in the same region enhance HbF yield, which improves thalassemia symptoms (Gorji et al. 2011; Lettre et al. 2008). C32T polymorphism in the first exon of HBS1L can also up-regulate HbF production in thalassemic patients through alteration of the binding motifs of AP-4 replication factor (Pandit et al. 2008; Uda et al. 2008).

GSTT1 and GSTM1 Polymorphisms Regular transfusions plus iron chelation comprises the standard treatment strategy for beta-thalassemia major. As a result of repetitive transfusions and ineffective erythropoiesis, iron overload and consequently destructive oxidation occur in various organs, especially heart and liver (Chakarov et al. 2014; Valko et al. 2007). A number of studies have shown that due to high reactive oxidant species (ROS) concentrations, erythrocytes of a thalassemic patient are at a higher risk of apoptosis. Glutathione S-transferase (GST) enzyme family forms a defense mechanism against such destruction (Chakarov et al. 2014). These enzymes are encoded by 16 genes and are divided into five classes: a (GSTA), p (GSTP), l (GSTM), h (GSTT), and f (GSTZ) (Sclafani et al. 2013). The null genotype in GTSM1 and GSTT1, with neither allele active, leads to lack of enzyme activity and increased sensitivity to oxidative stress (Hahn et al. 2010). This genotype has a prevalence of 23–62% across the world, 30% among Caucasians and more than 50% in the Chinese (Sclafani et al. 2013; Economopoulos and Sergentanis 2010). SNPs and deletions in the mentioned loci have been correlated with a decreased glutathione activity or total loss of it (Chakarov et al. 2014; Elhasid et al. 2010). These polymorphisms as well as the null genotype can play a role in tissue damage, including heart and liver, which is caused by iron overload in c-thalassemia patients (Sclafani et al. 2013).

123

Biochem Genet

The COL IAI Polymorphism Osteopenia and osteoporosis are key players in morbidity among thalassemia major (TM) patients (Toumba and Skordis 2010). There is a host of different factors leading to bone density reduction in TM, one of which could be a mutation in the gene for type I collagen a-chain (COL IAI) (Kostik et al. 2013). Type I collagen is the most abundant structural protein in the bone matrix and its polymorphisms have been associated with bone mineral density (BMD) (Mann and Ralston 2003; Pluijm et al. 2004). The regulator sequence of the mentioned gene is a known binding site for SP1 transcription factor, where a G[T mutation is reported to have a strong connection with osteoporosis in TM patients (Singh et al. 2013). The resulting altered SP1 affinity, the T allele carriers, produce more a1 collagen chain causing an imbalance between the a1:a2 chains, which in turn affects bone density (Kostik et al. 2013). A research by Singh in 2013 revealed that 19% of beta-thalassemia patients have the G/G genotype, 40% are heterozygous and 43% are homozygous (T/T genotype) (Singh et al. 2013).

HBBP1 Mutation A gene in the beta-globin gene cluster is HBBP1, where the rs2071348 mutation increases HbF levels as well as MCH, leading to milder thalassemia symptoms (Giannopoulou et al. 2012; Tomkins 2013). The findings of a study suggest that a mutation in HBBP1 (A/C) leads to elevated HbF levels in thalassemia and less severe symptoms but does not change response to hydroxyl-urea (Kerdpoo et al. 2014).

(AT)x(T)y Repeats Two of the determinants in c-globin chain synthesis rate are 30 HS1 (?179C[T) polymorphism in the (AT)xNy(AT)z motif in 50 HS and in (AT)x(T)y motif in -540 of HBB gene (Chen et al. 2010). A (AT)9(T)5 in the -530 HBB site affects promoter function, creating a binding site for the inhibitory factor BP1 (Kostik et al. 2013). The (AT)9(T)5 variation is usually concurrent with the thalassemic mutation G[A in codon 15 (cd15 G[A) (Elion et al. 1992; Arya et al. 2010). These events eventually lead to higher HbF levels and better clinical condition for the thalassemic intermediate or sickle cell patient as previously discussed (Dabke et al. Dabke et al. 2013).

Polymorphism in Exon 9 in Catalase Gene Catalase breaks hydrogen peroxide to water and oxygen, thus protecting cells against free radicals of oxygen (Casp et al. 2002). The gene CAT resides on the band 11p13 and consists of 12 introns and 13 exons (Lv et al. 2011). A number of

123

Biochem Genet

Fig. 1 Single nucleotide polymorphisms in transcription factors and their effect on c-globin gene expression. a b-globin chain gene on chromosome 11 consists of e, c, wb, d, and b genes, the expression of which is controlled by different transcription factors. In addition to transcription factors, over 600 mutations have been reported in beta-globin locus, among which 200 mutations are located on b-globin gene region, changing gene expression in b-thalassemia. Furthermore, polymorphisms in transcription factor genes such as BCL11A, HBS1L-MYB, and GATA-1 that play a role in the expression of beta and gamma chains are observed in patients with b-thalassemia and affect HbF production rate and change patient’s symptoms. b BCL11A gene on band 2p16 encodes a transcription factor that represses the cglobin gene expression. Rs11886868, rs766432, and rs4671393 polymorphisms on this gene are associated with up-regulation of fetal hemoglobin synthesis in b-thalassemia patients. c HBS1L-MYB intergenic polymorphisms (HMIP) on 6q23.3 such as rs4895441, rs28384513, and rs9399137 can also upregulate HbF and F-cell production, which improves thalassemia symptoms. HbF fetal hemoglobin, HBBP1 hemoglobin, beta pseudogene1, TRF2/TRF4 telomeric repeat binding factor 2/4, BCL11A B cell CLL/lymphoma 11A (zinc finger protein), KLF1 Kruppel-like factor 1, HBS1L HBS1-like translational GTPase, MYB myeloblastosis oncogene

mutations appear on exon 9, including two mutations causing acatalasemia (G113A and G5A) and a silent rs769217 (?22348 C[T) (Casp et al. 2002; Lv et al. 2011). A decline in catalase activity has been reported in patients with beta-thalassemia who

123

Biochem Genet

were also homozygous for the polymorphism rs769217. The mentioned enzymatic deficiency causes the cells to be more vulnerable to free radicals, exacerbating the thalassemia symptoms (Nagy et al. 2012).

Conclusions and Future Directions Thalassemia is a widespread disease with high mortality and morbidity rates and a wide range of symptoms. The onset of these symptoms and subsequent transfusions differs in each patient, and the reason for this phenomenon remains to be clarified. Different mutations, however, are proposed as a contributing factor (Fig. 1). Certain mutations, mostly in the beta-globin gene cluster affecting gamma globin production, could improve or exacerbate thalassemia symptoms. Various mutations in the genes HBS1L-MYB, BCL11A, and HBG2-Xmn1 are a few examples. In addition to b-globin gene, polymorphisms in other genes have been reported in TM patients such as exon 9 of CAT and in GST, especially GSTM1 and GSTT1, which affect the severity of iron overload conditions by influencing cell susceptibility to free radicals. Finding these polymorphisms and mutations in beta-thalassemia patients can contribute to a more accurate prognosis and probability of different symptoms for each patient. Eventually, this will help in planning more efficient prophylactic measures. Acknowledgments This paper is issued from the thesis of Abolfazl Ramezani, MSc student of hematology and blood banking. This work was financially supported by Grant IR. AJUMS. REC. TH93/ 15 from vice chancellor for Research Affairs of Ahvaz Jundishapur University of Medical Sciences. Compliance with Ethical Standards Conflict of interest The authors declare no conflict of interest.

References Alijani S, Alizadeh S, Kazemi A, Khatib ZK, Soleimani M, Rezvani M et al (2014) Evaluation of the effect of miR-26b up-regulation on HbF expression in erythroleukemic K-562 cell line. Avicenna J Med Biotechnol 6(1):53 Arya V, Agarwal S, Pradhan M (2010) Association of polymorphic pattern of the (AT)x(T)y motif of betaglobin gene in North Indian thalassemia patients with variable clinical expression. Indian J Hematol Blood Transfus 26(1):21–23 Bauer DE, Orkin SH (2011) Update on fetal hemoglobin gene regulation in hemoglobinopathies. Curr Opin Pediatr 23(1):1 Casp CB, She JX, Mccormack WT (2002) Genetic association of the catalase gene (CAT) with vitiligo susceptibility. Pigment Cell Res 15(1):62–66 Chakarov I, Vlaykova T, Slavov E, Marinov R, Chakarova P (2014) Role of serum pro-hepcidin and GSTM1 and GSTT1 null polymorphisms for estimation of the risk of myocardial siderosis in children and ‘‘young adults’’ with b-thalassemia major. Comp Clin Pathol 23(3):725–733 Chen W, Zhang X, Shang X, Cai R, Li L, Zhou T et al (2010) The molecular basis of beta-thalassemia intermedia in southern China: genotypic heterogeneity and phenotypic diversity. BMC Med Genet 11(1):31

123

Biochem Genet Dabke P, Colah R, Ghosh K, Nadkarni A (2013) Effect of cis acting potential regulators in the b globin gene cluster on the production of HbF in thalassemia patients. Mediterr J Hematol infect Dis 5(1):e2013012 Dassanayake RS, Mahadevan K, Gunawardene YI (2013) Development of single-strand conformational polymorphism to screen for mutations in hotspot regions of beta-globin gene of beta-thalassemia patients of Sri Lanka. SE Asian J Trop Med Public Health 44(1):114–123 Dehghanifard A, Shahjahani M, Galehdari H, Rahim F, Hamid F, Jaseb K et al (2013) Prenatal diagnosis of different polymorphisms of beta-globin gene in Ahvaz. Int J Hematol-Oncol Stem Cell Res 7(2):17–22 Economopoulos KP, Sergentanis TN (2010) GSTM1, GSTT1, GSTP1, GSTA1 and colorectal cancer risk: a comprehensive meta-analysis. Eur J Cancer 46(9):1617–1631 Ehteram H, Bavarsad MS, Mokhtari M, Saki N, Soleimani M, Parizadeh SM et al (2014) Prooxidantantioxidant balance and hs-CRP in patients with beta-thalassemia major. Clin Lab 60(2):207–215 Elhasid R, Krivoy N, Rowe JM, Sprecher E, Adler L, Elkin H et al (2010) Influence of glutathione S-transferase A1, P1, M1, T1 polymorphisms on oral busulfan pharmacokinetics in children with congenital hemoglobinopathies undergoing hematopoietic stem cell transplantation. Pediatr Blood Cancer 55(6):1172–1179 Elion J, Berg PE, Lapoumeroulie C, Trabuchet G, Mittelman M, Krishnamoorthy R et al (1992) DNA sequence variation in a negative control region 50 to the beta-globin gene correlates with the phenotypic expression of the beta s mutation. Blood 79(3):787–792 Fanis P, Kousiappa I, Phylactides M, Kleanthous M (2014) Genotyping of BCL11A and HBS1L-MYB SNPs associated with fetal haemoglobin levels: a SNaPshot minisequencing approach. BMC Genomics 15:108 Garner C, Tatu T, Game L, Cardon LR, Spector TD, Farrall M et al (2000) A candidate gene study of F cell levels in sibling pairs using a joint linkage and association analysis. GeneScreen 1(1):9–14 Giannopoulou E, Bartsakoulia M, Tafrali C, Kourakli A, Poulas K, Stavrou EF et al (2012) A single nucleotide polymorphism in the HBBP1 gene in the human b-globin locus is associated with a mild b-thalassemia disease phenotype. Hemoglobin 36(5):433–445 Gorji F, Hamid M, Arab A, Amirian A, Zeinali S, Karimipoor M (2011) Relationship between DNA polymorphisms at the BCL11A and HBS1L-MYB loci in b-Thalassemia patients with increased fetal hemoglobin levels. Sci J Blood Transfus Organ 8(3):149–157 Hahn T, Zhelnova E, Sucheston L, Demidova I, Savchenko V, Battiwalla M et al (2010) A deletion polymorphism in glutathione-S-transferase mu (GSTM1) and/or theta (GSTT1) is associated with an increased risk of toxicity after autologous blood and marrow transplantation. Biol Blood Marrow Transplant 16(6):801–808 Haj Khelil A, Moriniere M, Laradi S, Khelif A, Perrin P, Ben Chibani J et al (2011) Xmn I polymorphism associated with concomitant activation of Ggamma and Agamma globin gene transcription on a beta0-thalassemia chromosome. Blood Cells Mol Dis 46(2):133–138 Hardison RC, Chui DH, Giardine B, Riemer C, Patrinos GP, Anagnou N et al (2002) HbVar: a relational database of human hemoglobin variants and thalassemia mutations at the globin gene server. Hum Mutat 19(3):225–233 Hung CC, Su YN, Lin CY, Chang YF, Chang CH, Cheng WF et al (2008) Comparison of the mismatchspecific endonuclease method and denaturing high-performance liquid chromatography for the identification of HBB gene mutations. BMC Biotechnol 8:62 Kerdpoo S, Limweeraprajak E, Tatu T (2014) Effect of Swiss-type heterocellular HPFH from XmnI-Gc and HBBP1 polymorphisms on HbF, HbE, MCV and MCH levels in Thai HbE carriers. Int J Hematol 99(3):338–344 Kostik MM, Smirnov AM, Demin GS, Mnuskina MM, Scheplyagina LA, Larionova VI (2013) Genetic polymorphisms of collagen type I a1 chain (COL1A1) gene increase the frequency of low bone mineral density in the subgroup of children with juvenile idiopathic arthritis. EPMA J 4(1):1–8 Lettre G, Sankaran VG, Bezerra MAC, Arau´jo AS, Uda M, Sanna S et al (2008a) DNA polymorphisms at the BCL11A, HBS1L-MYB, and b-globin loci associate with fetal hemoglobin levels and pain crises in sickle cell disease. Proc Natl Acad Sci 105(33):11869–11874 Lettre G, Sankaran VG, Bezerra MA, Araujo AS, Uda M, Sanna S et al (2008b) DNA polymorphisms at the BCL11A, HBS1L-MYB, and beta-globin loci associate with fetal hemoglobin levels and pain crises in sickle cell disease. Proc Natl Acad Sci USA 105(33):11869–11874 Lv Y, Liao W, Luan Q, Wang H, Wang L, Li Q (2011) The polymorphism of catalase T/C codon 389 in exon 9 and vitiligo susceptibility: a meta-analysis. J Eur Acad Dermatol Venereol 25(8):955–958

123

Biochem Genet Mann V, Ralston SH (2003) Meta-analysis of COL1A1 Sp1 polymorphism in relation to bone mineral density and osteoporotic fracture. Bone 32(6):711–717 Menzel S, Garner C, Gut I, Matsuda F, Yamaguchi M, Heath S et al (2007) A QTL influencing F cell production maps to a gene encoding a zinc-finger protein on chromosome 2p15. Nat Genet 39(10):1197–1199 Musallam KM, Cappellini MD, Wood JC, Taher AT (2012) Iron overload in non-transfusion-dependent thalassemia: a clinical perspective. Blood Rev 26(Suppl 1):S16–S19 Nagy T, Csorda´s M, Ko´sa Z, Go´th L (2012) A simple method for examination of polymorphisms of catalase exon 9: rs769217 in Hungarian microcytic anemia and beta-thalassemia patients. Arch Biochem Biophys 525(2):201–206 Neishabury M, Zamani F, Keyhani E, Azarkeivan A, Abedini SS, Eslami MS et al (2013) The influence of the BCL11A polymorphism on the phenotype of patients with beta thalassemia could be affected by the beta globin locus control region and/or the Xmn1-HBG2 genotypic background. Blood Cells Mol Dis 51(2):80–84 Nguyen TK, Joly P, Bardel C, Moulsma M, Bonello-Palot N, Francina A (2010) The XmnI (G)gamma polymorphism influences hemoglobin F synthesis contrary to BCL11A and HBS1L-MYB SNPs in a cohort of 57 beta-thalassemia intermedia patients. Blood Cells Mol Dis 45(2):124–127 Pandit RA, Svasti S, Sripichai O, Munkongdee T, Triwitayakorn K, Winichagoon P et al (2008) Association of SNP in exon 1 of HBS1L with hemoglobin F level in b0-thalassemia/hemoglobin E. Int J Hematol 88(4):357–361 Pluijm SM, van Essen HW, Bravenboer N, Uitterlinden AG, Smit JH, Pols HA et al (2004) Collagen type I alpha1 Sp1 polymorphism, osteoporosis, and intervertebral disc degeneration in older men and women. Ann Rheum Dis 63(1):71–77 Sankaran VG, Orkin SH (2013) The switch from fetal to adult hemoglobin. Cold Spring Harb Perspect Med 3(1):a011643 Sclafani S, Calvaruso G, Agrigento V, Maggio A, Nigro VL, D’Alcamo E (2013) Glutathione S transferase polymorphisms influence on iron overload in b-thalassemia patients. Thalassemia Rep 3(1):e6 Sedgewick AE, Timofeev N, Sebastiani P, So JC, Ma ES, Chan LC et al (2008) BCL11A is a major HbF quantitative trait locus in three different populations with beta-hemoglobinopathies. Blood Cells Mol Dis 41(3):255–258 Singh K, Agarwal S, Gupta S (2013) An SP1-binding site polymorphism in the COLIAI gene: may be a strong predictor for low bone density in thalassemia major. Gene Ther Mol Biol 15:112–119 Stadhouders R, Aktuna S, Thongjuea S, Aghajanirefah A, Pourfarzad F, van Ijcken W et al (2013) HBS1L-MYB intergenic variants modulate fetal hemoglobin via long-range MYB enhancers. Blood 122(21):43 Svasti S, Masaki S, Penglong T, Abe Y, Winichagoon P, Fucharoen S et al (2010) Expression of microRNA-451 in normal and thalassemic erythropoiesis. Ann Hematol 89(10):953–958 Tomkins J (2013) Beta-globin pseudogene is functional after all. Creat Sci Update Toumba M, Skordis N (2010) Osteoporosis syndrome in thalassaemia major: an overview. J Osteoporos. doi:10.4061/2010/537673 Uda M, Galanello R, Sanna S, Lettre G, Sankaran VG, Chen W et al (2008) Genome-wide association study shows BCL11A associated with persistent fetal hemoglobin and amelioration of the phenotype of beta-thalassemia. Proc Natl Acad Sci USA 105(5):1620–1625 Valko M, Leibfritz D, Moncol J, Cronin MT, Mazur M, Telser J (2007) Free radicals and antioxidants in normal physiological functions and human disease. Int J Biochem Cell Biol 39(1):44–84 Wonkam A, Ngo Bitoungui VJ, Vorster AA, Ramesar R, Cooper RS, Tayo B et al (2014) Association of variants at BCL11A and HBS1L-MYB with hemoglobin F and hospitalization rates among sickle cell patients in Cameroon. PLoS One 9(3):e92506

123