Novel Point Mutation of the α2-Globin Gene (HBA2) and a Rare 2.4 kb Deletion of the α1-Globin Gene (HBA1), Identified in Two Chinese Patients with Hb H Disease

Detection of Hb H disease caused by a novel mutation and --SEA deletion using capillary electrophoresis

Background

Hb H disease is a serious type of α‐thalassemia which cause moderate anemia while misdiagnosis by routine genetic analysis in a rare or novel Hb H disease.

Methods

The study was done on three patients and one fetus in a suspected Hb H disease family. Hb analysis was carried out using capillary electrophoresis (CE), and hematological analysis was conducted with an automated cell counter. Common α‐ and β‐thalassemia mutations were detected by routine genetic analysis (gap‐PCR and RDB‐PCR). Novel mutation diagnostic methods were based on DNA sequencing.

Results

Capillary electrophoresis revealed clinical feature of classic Hb H disease in the proband, and hematology analysis showed moderate anemia (Hb 87 g/L). But routine genetic analysis was found that it was only a heterozygote for the ‐‐^SEA deletion. DNA sequencing of α‐globin genes (α1 and α2) identified the breakpoints between nts 34162 and 34171 at α2 gene, named CD 90‐93 (‐AGCTTCGG) mutation. The genotype of proband and fetus was the same ‐‐^SEA/‐α^CD90‐93. His father was homozygous for the novel mutation (‐α^CD90‐93/‐α^CD90‐93), and his mother was heterozygote for the ‐‐^SEA deletion.

Conclusions

Our study for the first time described the novel mutation CD 90‐93 (‐AGCTTCGG). CE is a way to avoid misdiagnosis of rare or novel Hb H disease.

Identification of Three Types of α-Thalassemia Deletion, -α21.9, -α2.4, and - -THAI, and Their Frequencies, in One Family in the Population of Southern Guangxi Zhuang Autonomous Region, People's Republic of China

Different types of deletional α-thalassemia (α-thal) have been reported by researchers in China. This study describes one family carrying -α^21.9 (NG_000006.1: g.14373_36299delinsGGGAAGGGTGGGTGGGAATAACAGCTTTT), -α^2.4 (NG_000006.1: g.36860_39251del) and - -^THAI (Thailand) (NG_000006.1: g.10664_44164del) alleles in Guangxi Zhuang Autonomous Region, People's Republic of China (PRC), and reports the frequencies of these types in the population of this region. The proband was a 4-year-old girl, who screened positive for thalassemia, although the thalassemia genotype results were normal when screened using the routine kits. Samples of the proband's parents were also collected to perform further analyses. Two real-time gap-polymerase chain reaction (gap-PCR) systems were designed for separate detection of - -^THAI and screening for -α^21.9 and -α^2.4. The genotype of the proband was -α^21.9/-α^2.4, and the two variants were inherited from her parents. In the frequency study, five - -^THAI, four -α^21.9 and 11 -α^2.4 positive individuals were detected in the 3410 random samples. Thus, allele frequencies of -α^21.9, - -^THAI and -α^2.4 in the population of southern Guangxi were determined as 0.059, 0.073 and 0.161%, respectively. This is the first report of an individual carrying the -α^21.9/-α^2.4 genotype, and the first report of the detection of -α^21.9, -α^2.4 and - -^THAI in a single family. The total frequency for these alleles was 0.293% in southern Guangxi, suggesting that the thalassemia clinical center in this region should utilize a screening kit that allows detection of these types of deletions for a more comprehensive evaluation of thalassemia risk.

Identification of the -α(2.4) Deletion in One Family and in One Hb H Disease Patient in Guangxi, People's Republic of China

The 2.4 kb (or -α(2.4)) deletion in the α-globin gene cluster (NG_000006.1) is an α(+)-thalassemia (α(+)-thal) allele. The molecular basis of -α(2.4) is a deletion from 36860 to 39251 of the α-globin gene cluster. It was reported by three research groups in 2005, 2012 and 2014, respectively. In routine thalassemia screening studies by this research group, we found an individual with the -α(2.4)/αα genotype and an Hb H (β4) disease patient whose genotype was - -(SEA)/-α(2.4). Samples from the parents of the carrier of the -α(2.4)/αα genotype were collected to perform pedigree analysis, and the proband's mother's genotype was diagnosed to be - -(SEA)/-α(2.4). The research revealed that the -α(2.4) allele exists in the population of southern Guangxi, People's Republic of China.

Rapid diagnosis of common deletional α-thalassemia in the Chinese population by qPCR based on identical primer homologous fragments

OBJECTIVE

In China, -(SEA), -α(3.7) and -α(4.2) are common deletional α-thalassemia alleles. Gap-PCR is the currently used detection method for these alleles, whose disadvantages include time-consuming procedure and increased potential for PCR product contamination. Therefore, this detection method needs to be improved. Based on identical-primer homologous fragments, a qPCR system was developed for deletional α-thalassemia genotyping, which was composed of a group of quantitatively-related primers and their corresponding probes plus two groups of qualitatively-related primers and their corresponding probes. In order to verify the accuracy of the qPCR system, known genotype samples and random samples are employed.

RESULT

The standard curve result demonstrated that designed primers and probes all yielded good amplification efficiency. In the tests of known genotype samples and random samples, sample detection results were consistent with verification results.

CONCLUSIONS

In detecting αα, -(SEA), -α(3.7) and -α(4.2) alleles, deletional α-thalassemia alleles are accurately detected by this method. In addition, this method is provided with a wider detection range, greater speed and reduced PCR product contamination risk when compared with current common gap-PCR detection reagents.