Hemoglobin, 35(1):84–86, (2011)Copyright © Informa Healthcare USA, Inc.ISSN: 0363-0269 print/1532-432X onlineDOI: 10.3109/03630269.2010.529744

SHORT COMMUNICATION

β+-THALASSEMIA TRAIT DUE TO A NOVEL MUTATION IN THE

β-GLOBIN GENE PROMOTER: −26 (A>C) [HBB c.−76A>C]

John S. Waye,1,2 Lisa M. Nakamura-Garrett,1 Barry Eng,1 Emmanuel

Kanavakis,3 and Joanne Traeger-Synodinos3

1Hamilton Regional Laboratory Medicine Program, Hamilton Health Sciences, Hamilton, Ontario,Canada2Department of Pathology and Molecular Medicine, McMaster University, Hamilton, Ontario, Canada3Department of Medical Genetics, University of Athens, St. Sophia’s Children’s Hospital, Athens, Greece

� We report the case of a woman with β+-thalassemia (β+-thal) trait, in which there were twosequence variants within the β-globin gene promoter: −54 (G>A) [HBB c.−104G>A] and −26(A>C) [HBB c.−76A>C]. Data from other patients indicate that the −54 substitution is a nonpathogenic sequence variant. Therefore, the β-thal phenotype is most likely due to the −26 mutationthat is adjacent to the conserved ATAA box.

Keywords β+-Thalassemia (β+-thal), Promoter mutation

The patient is a 32-year-old Canadian woman of unspecified ethnicitywho presented with mild β-thalassemia (β-thal) trait. The hematologicalindices are as follows: Hb 12.0 g/dL, MCV 73.7 fL, MCH 23.5 pg, RBC5.10 × 1012/L, Hb A2 5.2%, Hb F 0.5%. The β-globin gene was amplifiedby polymerase chain reaction (PCR) and sequenced in both orientationsusing the BigDyeTM Terminator Cycle Sequencing Kit and the ABI PRISMTM

3130 automated capillary sequencer (Applied Biosystems, Foster City, CA,USA. Sequence analysis of the entire gene revealed heterozygosity for twocommon sequence polymorphisms [codon 2 (CAC>CAT) and IVS-II-666(T>C)]. The only other changes were found within the promoter region ofthe β-globin gene at positions −54 (G>A) and −26 (A>C) relative to the

Received 29 July 2010; Accepted 17 September 2010.Address correspondence to Dr. John S. Waye, Department of Pathology and Molecular Medicine,

McMaster University Medical Centre, Hamilton, Ontario L8N 3Z5, Canada. Tel: +905-521-2100, ext.76273; Fax: +905-521-2651; E-mail: waye@hhsc.ca

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Mild β+-Thalassemia Mutation 85

-54 -26 Cap+1| | |

GGGAGGGCAGGAGCCAGGGCTGGGCATAAAAGTCAGGGCAGAGCCATCTATTGCTTACATTA C

FIGURE 1 Direct nucleotide sequence analysis of the β-globin gene showing the −54 (G>A) and −26(A>C) substitutions relative to the mRNA Cap site.

mRNA Cap site (Figure 1). These changes have not been reported as caus-ing β-thal (1), or as non pathogenic sequence variants. Family studies werenot possible to establish whether the sequence variants are in cis or trans.

In theory, the β-thal phenotype could be due to the −54 and/or the−26 sequence variants. The −54 variant is adjacent to the direct repeat ele-ment (DRE) (positions −53 to −32), which is thought to be an importantregulatory element for β-globin gene transcription (2). Several sequencevariants upstream or within the β-DRE have been implicated in β-thal,including −56 (G>C) (1,3), −50 (G>A) (4), and −42 (C>G) (5). In theGreek population, we have observed the −54 variant in several patientsamong the many thousands analyzed for β-globin gene mutations. Basedon hematological phenotypes in simple heterozygotes, as well as in com-pound heterozygotes with common β-thal mutations in trans (confirmedby linkage), this sequence variant is not associated with notable changesin hematological findings, indicating no changes (reduction) in the lev-els of β-globin synthesis (Table 1). Therefore, it is unlikely that the −54

TABLE 1 Hematological Profiles Associated With the −54 (G>A) Sequence Variant

PatientaSex-

GroupbHb

(g/dL)MCV(fL)

MCH(pg)

Hb A2(%)

Hb F(%) β Genotypec α Genotype

1 F-A 11.6 106.0 31.0 3.3 1.7 −54(G>A)/βA αα/αα

2 F-C 9.8 100.0 32.0 2.7 1.0 −54(G>A)/βA αα/αα

3 M-A 14.0 93.0 29.9 3.0 0.5 −54(G>A)/βA αα/αα

4 F-C 11.3 83.0 26.1 2.3 1.6 −54(G>A)/βA −α3.7/αα

5 F-C 10.3 60.0 19.4 5.7 3.9 −54(G>A)/IVS-II-745(C>G)d αα/αα

6 M-A 10.9 71.0 20.8 6.0 1.9 −54(G>A)/IVS-I-I(G>A)e αα/αα

7 F-C 12.2 66.0 21.4 6.1 2.0 −54(G>A)/IVS-II-1(G>A) αα/αα

aPatients 6, 1, and 5 represent three successive generations of a Greek family, confirming independentsegregation of the −54 sequence variant.

bA = adult; C = child.cHGVS nomenclature: −54 (G>A) [HBB c.–104G>A], IVS-II-745 (C>G) [HBB c. 316–106C>G], IVS-

II-1 (G>A) [HBB c.315+1G>A].dHematological values (average ± standard deviation) for adult carriers (N = 5) of the IVS-II-745

(C>G) mutation: MCV 68.5 ± 4.7 fL, MCH 21.1 ± 0.9 pg, Hb A2 5.1 ± 0.4%, Hb F 0.5 ± 0.4%.eHematological values (average ± standard deviation) for adult carriers (N = 5) of the IVS-II-1 (G>A)

mutation: MCV 64.3 ± 3.3 fL, MCH 20.2 ± 1.6 pg, Hb A2 5.5 ± 0.3%, Hb F 3.4 ± 1.6%.

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86 J.S. Waye et al.

contributes significantly to the β-thal phenotype of the patient described inthis report.

To date, twelve different β-thal alleles have been reported within andaround the conserved ATAA box (positions −31 to −28) of the β-globingene promoter (1,6). Included in this list are two mutations at positions−27 (A>C, A>G) (7,8) and one mutation at position −25 (G>C) (6).Accordingly, we propose that the β-thal phenotype of our patient is due tothe −26 sequence change. Presumably, as with other promoter mutations,the −26 mutation results in reduced transcription in cis.

Declaration of Interest: The authors report no conflicts of interest. Theauthors alone are responsible for the content and writing of this article.

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