Novel interactions of two α-Hb variants with SEA deletion α-thalassemia: hematological and molecular analyses.

OBJECTIVES

To report the hematological and molecular features as well as diagnostic aspects of the hitherto un-described interactions of two rare α-globin chain variants with α-thalassemia commonly found among Southeast Asian populations.

METHODS

The study was done on two adult Thai patients (P1 and P2) who had hypochromic microcytic anemia. Hb analysis was carried out using high performance liquid chromatography (HPLC) and capillary electrophoresis (CE). Mutations were identified by PCR and related techniques.

RESULTS

Hb analysis of P1 using HPLC showed a normal Hb pattern, but CE demonstrated an abnormal peak at zone 7. DNA sequencing identified a CCG-CTG mutation at codon 95 of the α2 globin gene corresponding to the Hb G-Georgia [α95(G2)Pro → Leu(α2)] previously undescribed in the Thai population. In contrast, Hb analysis of P2 demonstrated an abnormal peak not fully separated from Hb A on HPLC, but not on CE. DNA analysis identified the rarely described Hb Nakhon Ratchasima [α63(E12)Ala → Val(α2)] mutation. Routine DNA analysis detected the SEA deletion α-thalassemia in trans to the Hb variants in both cases. Hematological parameters were compared with those of patients with compound heterozygote for other α-globin variants and α-thalassemia previously documented.

CONCLUSIONS

Identification of the patients confirmed that interaction of these rare Hb variants with α-thalassemia does not lead to the Hb H disease. Differentiation of these two Hb variants from other clinically relevant hemoglobinopathies in a routine setting is, however, necessary. This can be accomplished using a combined Hb-HPLC and CE analysis followed by PCR-RFLP assays.