Molecular and hematological characteristics of a novel form of α-globin gene triplication: the hemoglobin St.Luke's-Thailand [α95(G2)Pro→Arg] or Hb St. Luke's [A2] HBA2.

OBJECTIVES

This study aims to report a hitherto un-described α-globin gene triplicated allele with a novel hemoglobin (Hb) variant on α2-globin gene, Hb St.Luke's-Thailand [α95(G2)Pro-Arg].

DESIGNS AND METHODS

A study was done on a 1.5-year-old Thai boy who showed pallor and jaundice after birth. Hb analysis was performed by HPLC and capillary electrophoresis. cDNAs of the two α-globin genes were analyzed by sequencing and novel diagnostic methods based on PCR-RFLP and multiplex PCR assays were developed.

RESULTS

Hb analysis by both HPLC and capillary electrophoresis revealed unknown variants for Hb A (amounting to 9.0 and 9.4%) and Hb A2 (0.7 and 0.6%). cDNA analysis of α-globin genes revealed a normal α1-globin gene sequence and a CCG (Pro) to CGG (Arg) mutation at codon 95 of the α2-globin gene leading to the Hb St.Luke's-Thailand or Hb St. Luke's [A2] HBA2: c.287C>G. DNA analysis of the patient and his mother identified the in cis α-globin gene triplication. This novel orientation of α-globin gene could be confirmed by PCR-NlaIV restriction digestion or a multiplex allele specific PCR assay developed.

CONCLUSIONS

A relatively lower percentage of the Hb St.Luke's-Thailand due to a HBA2 gene mutation could be explained by a linked anti-3.7 α-globin gene triplication. Clinical and hematological features, effect of α-globin gene triplication on the phenotypic expression of Hb St.Luke's-Thailand and diagnostics using combined HPLC, capillary electrophoresis and molecular techniques were presented.