Prenatal control of nondeletional α -thalassemia: first experience in mainland China

Thalassaemia in China

Because of successful thalassaemia prevention programmes in resource-rich countries and it's huge population China now has the greatest number of new cases of thalassaemia globally as well as more people with thalassaemia than any other country. 30 million Chinese have thalassaemia-associated mutations and about 300,000 have thalassaemia major or intermedia requiring medical intervention. Over the past 2 decades there has been tremendous economic growth in China including per capita spending on health care. There is now nation-wide availability and partial or full insurance for prenatal genetic testing, RBC-transfusions, iron-chelating drugs and haematopoietic cell transplants. Prenatal screening and educational programmes have reduced the incidence of new cases. However, substantial challenges remain. For example, regional differences in access to medical care and unequal economic development require innovations to reduce the medical, financial and psychological burdens of Chinese with thalassaemia and their families. In this review we discuss success in preventing and treating thalassaemia in China highlighting remaining challenges. Our discussion has important implications for resource-poor geospaces challenged with preventing and treating thalassaemia.

Identification of Three Families Carrying Hb Anti-Lepore Hong Kong Variant in Guangxi, China, and Analysis of Their Hematological Data

Thalassemia is a single-gene genetic disease with a high incidence in southern China. To prevent and control thalassemia, the most commonly used procedure is hematology testing and hemoglobin (Hb) analysis, followed by thalassemia gene analysis in positive individuals. During routine testing for thalassemia, we identified three individuals with Hb A₂ levels of >10.0%. The results of conventional thalassemia gene analysis of these individuals cannot explain this feature, and there is a possibility of carrying novel thalassemia gene variants. Therefore, we collected samples from these three families for further analysis of the thalassemia gene. The research team used multiplex ligation-dependent probe amplification (MLPA) to analyze the three families, and the analysis results showed that their molecular biological characteristics were similar to those of Hb Anti-Lepore Hong Kong (NG_000007.3: g.63210_70621dup). Then, gap-polymerase chain reaction (gap-PCR) and sequencing methods were used for verification, and it was confirmed that the variant carried by these three families was indeed Hb Anti-Lepore Hong Kong. Three individuals carrying both the - -^SEA (Southeast Asian) and Hb Anti-Lepore Hong Kong variants were also detected in this study, and these individuals had slightly lower Hb A₂ results than those carrying Hb Anti-Lepore Hong Kong alone. Further analyses revealed that the carrier rate of this variant is about 0.03% in the population, thus identifying it as a rare variant.

Genetic counseling and prenatal decision for hemoglobin H disease caused by the rare α2 codon 30 (-GAG) (HBA2: c.91_93delGAG) mutation and the SEA deletion: Case series study

OBJECTIVE

We report a rare mutation on the α2-globin gene, HBA2: c.91_93delGAG and its potential functions.

CASE REPORT

We mainly described four patients with hemoglobin (Hb) H disease caused by the rare mutation and the SEA deletion but diversity in clinical presentation. Two had survived to adulthood with normal physical and mental development, except for mild anemia. However, two were children, who had more severe clinical manifestations. One child had developmental disorders of speech and language and mild growth retardation, and the other child suffered from severe hemolytic crises precipitated by infection and received blood transfusion.

CONCLUSION

This study is of great significance for clinicians to provide genetic counseling to couples at-risk of having offspring with Hb H disease and let them make the pregnancy decision, particularly reduce the occurrence of severe Hb H disease.

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.

Fetal Anemia and Hydrops Fetalis Associated with Homozygous Hb Constant Spring (HBA2: c.427T > C)

Hb Constant Spring (Hb CS, HBA2: c.427T > C) is a common nondeletional α-thalassemia (α-thal) that results from a nucleotide substitution at the termination codon of the α2-globin gene. Homozygosity for Hb CS (α(CS)α/α(CS)α) is relatively rare, and generally characterized with mild hemolytic anemia, jaundice, and splenomegaly. In this report we present a fetus with cardiomegaly, pericardial effusion, enlarged placenta and increased middle cerebral artery-peak systolic velocity (MCA-PSV) at 24 weeks' gestation. Fetal blood sampling revealed the severe anemia [hemoglobin (Hb) level being 4.8 g/dL] and Hb H (β4) disease-like hematological findings with Hb Bart's (γ4) level of 17.9%. DNA sequencing of the α-globin genes found that both partners were Hb CS carriers and the fetus was an Hb CS homozygote. Therefore, this was a rare case of homozygous Hb CS which demonstrated an unusual and serious anemia and hydrops fetalis in utero.

Molecular Epidemiological Investigation of Thalassemia in the Chengdu Region, Sichuan Province, Southwest China

Thalassemia is the most common inherited disease in southern China. However, this disorder is usually ignored by the health system in the Sichuan Province due to the lack of epidemiological data. To provide basic epidemiological data for thalassemia screening, genetic counseling, and prenatal diagnosis (PND) in the Chengdu region, a total of 3262 healthy subjects were assessed by complete blood count (CBC), reverse dot-blot gene chip, gap-polymerase chain reaction (gap-PCR), and PCR-DNA sequencing. A frequency of heterozygous thalassemia of 3.43% (112/3262) was found, of which 2.21% (72/3262) patients carried α-thalassemia (α-thal), 1.19% (39/3262) β-thalassemia (β-thal) and 0.3% (1/3262) hereditary persistence of fetal hemoglobin (Hb) (HPFH)/δβ-thalassemia (δβ-thal). Four types of α-thal mutations were found, the most prevalent being - -(SEA) (68.06%), followed by -α(3.7) (rightward deletion, 25.0%), Hb Quong Sze (Hb QS; HBA2: c.377 T > C) (4.17%), and -α(4.2) (leftward deletion, 2.78%). The seven β-thal mutations included: codons 41/42 (-TTCT), HBB: c.126_129delCTTT (13/39, 33.33%); codon 17 (A > T), HBB: c.52 A > T (11/39, 28.95%); IVS-II-654 (C > T), HBB: c.316-197 C > T (9/39, 23.68%); -28 (A > G), HBB: c.-78 A > G (3/39, 7.69%); -29 (A > G), HBB: c.-79 A > G (1/39, 2.56%); codons 27/28 (+C), HBB: c.84_85insC (1/39, 2.56%), and the rare IVS-II-850 (G > T), HBB: c.316-1 G > T (1/39, 2.56%). Only one case of the Southeast Asian HPFH deletion was found. This is the first detailed molecular epidemiological survey of thalassemia in the Chengdu region, Sichuan Province, People's Republic of China (PRC).

Co-inheritance of α-thalassaemia and β-thalassaemia in a prenatal screening population in mainland China

Objective

To determine the prevalence of α-thalassaemia in β-thalassaemia individuals in a Chinese population.

Methods

The standard diagnostic marker for β-thalassaemia was elevation of the Hb A2 level (>3.5%) with low mean corpuscular volume. The common α-thalassaemia mutations were studied by molecular analysis in all identified β-thalassaemia carriers.

Results

A prevalence rate of 3.3% for β-thalassaemia was found in our population; α- and β-thalassaemia interactions were found to co-exist in 17.8% of the β-thalassaemia carriers. The -SEA deletion was the most common α-thalassaemia mutation co-inherited with β-thalassaemia, followed by the -α3.7 deletion, the -α4.2 deletion, Hb Quong Sze, and Hb Constant Spring.

Conclusion

Our results suggest that it could be valuable to study co-existing α-globin mutations in subjects with β-thalassaemia trait in a prenatal screening programme, especially in populations with a high prevalence of haemoglobinopathies.

Prevalence and molecular characterization of structural hemoglobin variants in the Dongguan region of Guangdong province, southern China

The aim of the present study was to find the most prevalent structural hemoglobin (Hb) variants in southern China and to present hematological and molecular data of abnormal Hbs in the population from southern China. The type and frequency of structural Hb variants and their hematological and molecular characteristics were identified in 131 individuals from 30,848 unrelated partners who were referred to the prenatal clinic of Dongguan Maternal & Children Health Hospital, Dongguan, Guangdong, People's Republic of China (PRC) from 2011 to 2013. α-Globin or β-globin chain variants were screened using a capillary electrophoresis (CE) system, and α-globin or β-globin gene mutations were confirmed using sequencing techniques. The gene frequency of Hb variants was 0.4% (131/30,848). The most common α-globin variants were Hb Constant Spring (Hb CS, HBA2: c.427T > C) (0.2%), followed by Hb Q-Thailand (HBA1: c.223G > C) and Hb G-Honolulu (HBA2: c.91G > C). The most common β-globin variant was Hb E (HBB: c.79G > A) (0.09%), followed by Hb New York (HBB: c.341T > A). Our results provide a detailed prevalence and molecular characterization of abnormal Hbs in the population of the Dongguan region. These findings have important implications for a region with a high frequency of α- and β-thalassemias.