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.

First report of the spectrum of δ-globin gene mutations among women of reproductive age in Fujian area-Discrimination of δ-thalassemia, α-thalassemia, and Iron Deficiency Anemia

Background

Low HbA₂ level is an underlying of δ‐thalassemia, α‐thalassemia, and IDA. Interactions of these disorders can generate a wide spectrum of phenotype, which will pose diagnostic conundrum for clinical assessment, carrier screening, and genetic counseling.

Methods

Subjects with HbA₂ levels below 2.0% with normal or reduced hematological parameters were recruited for further investigation. δ‐globin gene mutations were identified by DNA sequencing of the HBD gene. Serum ferritin (SF) concentration was determined by the chemiluminescent microparticle immunoassay. The three common deletional α‐thalassemia (‐‐^SEA/αα, ‐α^3.7/αα, and ‐α^4.2/αα) were detected using Gap‐PCR, detection of the point mutations in the three nondeletional α‐thalassemia (α^CSα/αα,α^QSα/αα,α^WSα/αα), and the 17 common β‐thalassemia was performed using reverse dot blot hybridization (RDB).

Results

We had characterized the δ‐globin gene mutations in 20 cases, revealing a frequency of 0.4% in the women of reproductive age (20/4 792). Two previously known mutations:‐77 T > C and −30 T > C and 3 novel δ‐globin gene defects: −44G > A,CD87C > T, and CD134T > A were found. In the selected cases, we also found 85 cases confirmed with (51.2%,85/166) IDA and 39 cases (23.5%,39/166) with common α‐thalassemia. Subjects with δ‐thalassemia had statistically higher levels of Hb, MCV, and MCH compared with other two groups, whereas statistically lower levels of RDW were seen in δ‐thalassemia group. What's more, statistically higher levels of SF were seen in δ‐thalassemia group, compared with IDA groups.

Conclusion

We reported the spectrum of δ‐thalassemia mutations for the first time with the frequency of 0.4% among women of reproductive age in Fujian area and found that −77T > C mutation was the most common mutation, followed by −30T > C mutation. What's more, 3 novel δ‐globin gene defects: −44G > A,CD87C > T and CD134T > A were found. A thorough analysis of the hematological, electrophoretic characterization, and the level of SF was needed to suspect and further investigate the existence of IDA, α‐thalassemia, and δ‐thalassemia.

Analysis of deletional hereditary persistence of fetal hemoglobin/δβ-thalassemia and δ-globin gene mutations in Southerwestern China

Background

Deletional hereditary persistence of fetal hemoglobin (HPFH)/δβ‐thalassemia and δ‐thalassemia are rare inherited disorders which may complicate the diagnosis of β‐thalassemia. The aim of this study was to reveal the frequency of these two disorders in Southwestern China.

Methods

A total of 33,596 subjects were enrolled for deletional HPFH/δβ‐thalassemia, and positive individuals with high fetal hemoglobin (Hb F) level were diagnosed by multiplex ligation‐dependent probe amplification (MLPA). A total of 17,834 subjects were analyzed for mutations in the δ‐globin gene. Positive samples with low Hb A₂ levels were confirmed by δ‐globin gene sequencing. Furthermore, the pathogenicity and construction of a selected δ‐globin mutation were analyzed.

Results

A total of 92 suspected cases with Hb F ≥5.0% were further characterized by MLPA. Eight different deletional HPFH/δβ‐thalassemia were observed at a frequency of 0.024%. In addition, 195 cases suspected to have a δ‐globin gene mutation (Hb A₂ ≤2.0%) were characterized by molecular analysis. δ‐Globin gene mutation was found at a frequency of 0.49% in Yunnan. The pathogenicity and construction for a selected δ‐globin mutation was predicted.

Conclusion

Screening of these two disorders was analyzed in Southwestern China, which could define the molecular basis of these conditions in this population.