Diagnosis of a Family with the Novel -α(21.9) Thalassemia Deletion

Prevalence and molecular characterization of common thalassemia among people of reproductive age in the border area of Guangxi-Yunnan-Guizhou province in Southwestern China

Objectives: Thalassemia, the most common global monogenetic disorder, is highly prevalent in southern China. Epidemiological and molecular characterization of thalassemia is important for designing appropriate prevention strategies in high-risk areas, especially the border area of Guangxi-Yunnan-Guizhou province in southwestern China.Methods: We recruited 38812 reproductive age couples and screened them for thalassemia. Routine blood tests as well as hemoglobin components and levels were evaluated. In addition, suspected thalassemia were identified by gap polymerase chain reaction (Gap-PCR) and PCR-based reverse dot blot (PCR-RDB).Results: The overall prevalence of thalassemia was 26.76%. Specifically, incidences of α-thalassemia, β-thalassemia, and concurrent α- and β-thalassemia were 17.52%, 6.92%, and 2.32%, respectively. The diagnosed α-thalassemia anomalies were associated with six gene mutations and 25 genotypes. The β-thalassemia anomalies were associated with 12 gene mutations and 15 genotypes. Moreover, among the 1799 concurrent mutated α- and β-thalassemia genes, 95 different genotypes were identified. Couples in which both partners were positive for α-thalassemia and β-thalassemia isotypes were 8.80% and 2.08%, respectively. The proportion of couples at a risk of having children with thalassemia major or intermedia was high.Conclusions: This study elucidates on the prevalence and molecular characterization of thalassemia in the border area of Guangxi-Yunnan-Guizhou provinces. These findings provide valuable baseline data for genetic counseling and prenatal diagnosis, with the overarching goal of preventing and controlling severe thalassemia.

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 a new 3.8kb deletional α thalassemia and detection of the deletion fragment]

OBJECTIVE

To report the identification of a novel 3.8-kb deletion that caused α thalassemia and establish the method for detecting the deletion fragment.

METHODS

Peripheral blood samples were collected from the proband and his mother for analysis of the hematological parameters and routine test for thalassemia genes. For the sample with an inconsistency between the genotyping results and phenotypic analysis results, a specific gap-PCR was employed to identify the rare or novel mutations.

RESULTS

A novel 3814-bp deletion causing α thalassemia was found in the proband and his mother, who had genotypes of -α4.2/-α3.8 and αα/-α3.8, respectively.

CONCLUSION

We identified a 3.8-kb deletion in the α-globin gene cluster that caused α thalassemia, and this finding enriches the α thalassemia gene mutation spectrum. Specific gap-PCR offers a convenient and efficient means for for detecting this deletion fragment.

A Novel Mutation of the α2-Globin Gene Causing α+-Thalassemia: Hb Nanning (HBA2: c.369_370delinsGA)

We report a novel mutation on the α2-globin gene, Hb Nanning (HBA2:c.369_370delinsGA) detected in a Chinese family. This mutation gives rise to a previously undescribed hemoglobin (Hb) variant that was undetectable by various separation techniques. Both carriers of the mutation have mean corpuscular volume (MCV) and mean corpuscular Hb (MCH) values that are below normal, as would be predicted for an α⁺-thalassemia (α⁺-thal) patient.

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.

Identification of a variation in the IVSII of α2 gene and its frequency in the population of Guangxi

OBJECTIVE

During thalassemia screening, a previously unidentified α2 gene variation in α-globin gene cluster was isolated. This variation was distinct from other variations known to confer thalassemia as assessed by conventional thalassemia genotype analysis. Because the sample in the thalassemia screening was positive (MCV=83.6fL, MCH=26.1pg/cell, Hb=11.3g/dL), further analysis was required.

MATERIAL AND METHODS

MLPA (multiplex ligation-dependent probe amplification) and sequencing were used for analysis, and a qPCR system was designed for the frequency study.

RESULTS

The MLPA result showed that there was a mutation or small fragment deletions between 34247 (160bp probe) and 34618 (196bp probe) in α-globin gene cluster (NG_000006.1). Through sequencing, this variation was identified as HBA2: c.301-24delGinsCTCGGCCC. The gene polymorphisms similar to HBA2:c.301-24delGinsCTCGGCCC are α121 and α212. Since α212 is unrelated to microcytosis, and the structure of HBA2: c.301-24delGinsCTCGGCCC is similar to α212, this change is more appropriately considered as a polymorphism. The allele frequency of HBA2: c.301-24delGinsCTCGGCCC is 0.184% in this region.

CONCLUSIONS

There is a certain ratio for HBA2:c.301-24delGinsCTCGGCCC carriers among the Chinese population. The HBA2:c.301-24delGinsCTCGGCCC variant results in an abnormal result from MLPA analysis. Investigators performing thalassemia screening in Guangxi region should be aware of the HBA2:c.301-24delGinsCTCGGCCC variant to avoid misinterpretation of the MLPA results.