Case report: Identification of a novel triplication of alpha-globin gene by the third-generation sequencing: pedigree analysis and genetic diagnosis

BACKGROUND

Thalassemia, a common autosomal hereditary blood disorder worldwide, mainly contains α- and β-thalassemia. The α-globin gene triplicates allele is harmless for carriers, but aggravates the phenotype of β-thalassemia. Therefore, it is particularly crucial to accurately detect the structural variants of α-globin gene clusters.

CASE REPORT

We reported a 28-year-old man, the proband, with microcytic hypochromic anemia. From pedigree analysis, his mother and sister had hypochromic microcytosis, and his father was normal. Genetic testing of thalassemia identified a novel α-globin gene triplicate named αααanti4.2del726bp (NC_000016.10:g.170769_174300dupinsAAAAAA) by third-generation sequencing (TGS) in the proband and his father, which was further validated by multiplex ligation-dependent probe amplification (MLPA) and Sanger sequencing. The genotypes of the proband's mother and sister were both -α3.7/αα compounded with heterozygous HBB:c.126_129delCTTT. They were categorized as silent α-thalassemia with co-inheritance of β-thalassemia trait. The proband's genotype additionally had the α-globin gene triplicates compared with his mother and sister, which increased the imbalance between α/β-globin, so the proband had more severe hematological parameters. The proband's wife was diagnosed as HBA2:c.427T > C heterozygosis, and his daughter had the novel α-globin gene triplicates compounded with HBA2:c.427T > C, therefore the girl might be asymptomatic.

CONCLUSION

The identification of the novel α-globin gene triplicates provides more insight for the research of thalassemia variants and indicates that TGS has significant advantages on genetic testing of thalassemia for the reliability, accuracy and comprehensiveness.

Production and Characterization of K562 Cellular Clones Hyper-Expressing the Gene Encoding α-Globin: Preliminary Analysis of Biomarkers Associated with Autophagy

One of the most relevant pathophysiological hallmarks of β-thalassemia is the accumulation of toxic α-globin chains inside erythroid cells, which is responsible for their premature death (hemolysis). In this context, the availability of an experimental model system mimicking the excess in α-globin chain production is still lacking. The objective of the present study was to produce and characterize K562 cellular clones forced to produce high amounts of α-globin, in order to develop an experimental model system suitable for studies aimed at the reduction of the accumulation of toxic α-globin aggregates. In the present study, we produced and characterized K562 cellular clones that, unlike the original K562 cell line, stably produced high levels of α-globin protein. As expected, the obtained clones had a tendency to undergo apoptosis that was proportional to the accumulation of α-globin, confirming the pivotal role of α-globin accumulation in damaging erythroid cells. Interestingly, the obtained clones seemed to trigger autophagy spontaneously, probably to overcome the accumulation/toxicity of the α-globin. We propose this new model system for the screening of pharmacological agents able to activate the full program of autophagy to reduce α-globin accumulation, but the model may be also suitable for new therapeutical approaches targeted at the reduction of the expression of the α-globin gene.

The hemoglobinopathies, molecular disease mechanisms and diagnostics

Hemoglobinopathies are the most common monogenic disorders in the world with an ever increasing global disease burden each year. As most hemoglobinopathies show recessive inheritance carriers are usually clinically silent. Programmes for preconception and antenatal carrier screening, with the option of prenatal diagnosis are considered beneficial in many endemic countries. With the development of genetic tools such as Array analysis and Next Generation Sequencing in addition to state of the art screening at the hematologic, biochemic and genetic level, have contributed to the discovery of an increasing number of rare rearrangements and novel factors influencing the disease severity over the recent years. This review summarizes the basic requirements for adequate carrier screening analysis, the importance of genotype–phenotype correlation and how this may lead to the unrevealing exceptional interactions causing a clinically more severe phenotype in otherwise asymptomatic carriers. A special group of patients are β‐thalassemia carriers presenting with features of β‐thalassemia intermedia of various clinical severity. The disease mechanisms may involve duplicated α‐globin genes, mosaic partial Uniparental Isodisomy of chromosome 11p15.4 where the HBB gene is located or haplo‐insufficiency of a non‐linked gene SUPT5H on chromosome 19q, first described in two Dutch families with β‐thalassemia trait without variants in the HBB gene.

Third-generation sequencing: A novel tool detects complex variants in the α-thalassemia gene

OBJECTIVE

Thalassemia is a monogenic disorder with a high carrier rate in the southern region of China. Most laboratories currently follow the protocol of testing hematologic indicators in individuals with positive hematologic indicators and then using the hot-spot mutation test kit. A novel thalassemia gene test is performed if there is a mismatch between the hematology and hot-spot mutation test results. However, due to the large population in southern China, some individuals carry complex α-globin gene cluster (CAGC) variants in NG_000006.1, which are difficult to detect using conventional thalassemia genetic analysis protocols, leading to missed or false genetic test results for individuals carrying these complex α-globin gene cluster variants. When an individual carries a complex α-thalassemia gene variant, and an individual carries a β- thalassemia gene variant, there may be clinical symptoms that might complicate clinical consultation and prenatal diagnosis if not accurately detected. Third-generation sequencing (TGS) enables long-read single-molecule sequencing with high detection accuracy, and long-length DNA chain reads in high-fidelity reads mode. TGS can be used to analyze high homology and rich GC DNA sequences.

RESULTS

Four samples that showed abnormalities in the thalassemia genetic test were studied using TGS, revealing that they carried genotypes with complex α-globin gene cluster variants, one of which was a complex variant αα anti3.7 α anti3.7 α 17.2.

CONCLUSIONS

TGS detects complex α-globin gene cluster variants. This study may provide a reference protocol for the use of TGS for the detection of complex α-globin gene cluster variants. TGS can reveal individuals with complex α-thalassemia genotypes in the population and improve the accuracy of genetic counseling and prenatal diagnosis.

Comparison of methodologies to detect hemoglobinopathy carriers in a multi-ethnic sperm donor population

An estimated 7% of the world's population are carriers for a hemoglobin disorder. Current guidelines recommend carrier screening by complete blood count, with follow-up hemoglobin electrophoresis or fractionation based on abnormal result or ethnicity. Advances in molecular genetic testing are thought to increase carrier detection. This study compares carrier screening methodologies in a multi-ethnic sperm donor population. A retrospective analysis was conducted using data from a US sperm bank. All men underwent carrier screening for hemoglobin disorders via complete blood count, hemoglobin fractionation, and molecular testing. Results were compared using counts and percentages. McNemar's exact test was used to examine differences in the marginal probabilities of screening methodologies. Of the 438 tested, 25 (5.7%) were identified as carriers of at least one hemoglobin disorder by molecular testing. Seventeen (68%) of those carriers were missed by recommended methods. No identified carriers were detected by recommended methods but missed by molecular testing. The difference between these discordant pairs was significant (p-value < 0.001). The majority (44%) of carriers were mixed ethnicity, followed by 36% White. Results indicate that molecular screening methodologies have a greater ability to detect carriers of hemoglobin disorders compared to currently recommended methods in a multi-ethnic population.

Prevalence of globin gene modifiers encountered in fetuses during antenatal diagnosis of hemoglobinopathies

INTRODUCTION

The hemoglobinopathies are the commonest group of single gene disorders in the Indian subcontinent. Although genetic modifiers are known to have a remarkable effect on phenotypic expression, the effects of the possible co-inheritance of different modifiers are not taken into account during prenatal diagnosis. The present study was undertaken to look for the frequency of globin gene modifiers like the types of β-globin gene mutations, α thalassemia, α gene triplication, and the Xmn1 polymorphism in fetuses during antenatal diagnosis of hemoglobinopathies.

MATERIALS AND METHODS

A total of 580 fetuses with different diagnoses were screened for the presence of genetic modifiers.

RESULTS

Twenty-two different β-globin gene mutations were identified of which 3.5% were milder mutations. Among the affected fetuses, 29.6% of the β-thalassemia major and 52.9% of the sickle cell anemia (SCA) fetuses had one genetic modifier while 3.7% of the β-thalassemia major and 41.1% of the SCA fetuses had co-inherited two modifiers. α-gene triplication was detected in 16 (3.5%) β-thalassemia/sickle cell heterozygous and normal fetuses of which 5 babies (2 β-thalassemia heterozygous and 3 normal) could be followed up. Of the 2 β-thalassemia heterozygous babies, one had a severe clinical presentation.

CONCLUSION

Many fetuses had one or two gene modifiers. However, the impact of these on ameliorating the severity of the disease could not be evaluated as all the fetuses with β thalassemia major or sickle cell disease were terminated. Parents having heterozygous fetuses with α gene triplication should be followed up periodically after birth for better management of these babies.