Prospective screening for δ-hemoglobinopathies associated with decreased hemoglobin A2 levels or hemoglobin A2 variants: A single center experience

BACKGROUND

δ-hemoglobinopathies may lead to misdiagnosis of several thalassemia syndromes especially β-thalassaemia carrier, it is important to evaluate the δ-globin gene defects in areas with high prevalence of globin gene disorders. We describe a prospective screening for δ-hemoglobinopathies in a routine setting in Thailand.

METHODS

Study was done on a cohort of 8,471 subjects referred for thalassemia screening, 317 (3.7%) were suspected of having δ-globin gene defects due to reduced hemoglobin (Hb) A₂ levels and/or appearance of Hb A₂-variants on hemoglobin analysis. Hematologic and DNA analysis by PCR and related assays were carried out.

RESULTS

DNA analysis of δ-globin gene identified seven different δ-globin mutations in 24 of 317 subjects (7.6%). Both known mutations; δ^-77(T>C) (n=3), δ^-68(C>T) (n=1), δ^-44(G>A) (n=8), Hb A₂-Melbourne (n=5), δ^{IVSII-897(A>C)} (n=5), and Hb A₂-Troodos (n=1) and a novel mutation; the Hb A₂-Roi-Et (n=1) were identified. This Hb A₂-Roi-Et, results from a double mutations in-cis, δ^{CD82(AAG>AAT)} and δ^{CD133(GTG>ATG)}, was interestingly found in combination with an in trans, 12.6 kb deletional δβ⁰-thalassemia in an adult Thai woman who had no Hb A₂ and elevated Hb F. A multiplex-allele-specific PCR was developed to detect these novel δ-globin gene defects.

CONCLUSIONS

The result confirms a diverse heterogeneity of δ-hemoglobinopathies in Thailand which should prove useful in a prevention and control program of thalassemia in the region.