The Current Status of β-Thalassemia Major in Mainland China

Misdiagnosis of β-Thalassemia Major Due to Chinese Gγ+(Aγδβ)0-Thalassemia Combined with β0-Thalassemia

δβ-thalassemia is a rare type of thalassemia characterized by increased Hb F levels, including mainly Chinese Gγ(Aγδβ)0-thalassemia, Yunnanese Gγ(Aγδβ)0-thalassemia, Cantonese Gγ(Aγδβ)0-thalassemia in China. Due to the low rate of δβ-thalassemia carriers, there are few reports of δβ-thalassemia combined with β-thalassemia causing β-thalassemia major. Herein, we described the combination of Chinese Gγ(Aγδβ)0-thalassemia and β-thalassemia leading to β-thalassemia major in a Chinese patient. Hemoglobin analysis was performed by capillary electrophoresis (CE). Routine genetic analysis was carried out by gap-polymerase chain reaction (Gap-PCR) and PCR and reverse dot blot (PCR-RDB). Multiple ligation-dependent probe amplification (MLPA) was used to detect the large deletion, and Gap-PCR confirmed the deletion. A CE result showed an elevated Hb F level of 98.7% and 11.7% in the proband and her mother, but the proband was diagnosed with βCD17M/βCD17M using routine genetic analysis. However, her father was heterozygous for CD17 in β-globin, and her mother was detected as SEA heterozygous. The further analysis presented that the proband had actually missed the diagnosis of Chinese Gγ(Aγδβ)0-thalassemia by MLPA and PCR-RDB. Finally, the genotype of the proband was corrected from βCD17M/βCD17M to βCD17M/βGγ(Aγδβ)0. This is the first report of Chinese Gγ(Aγδβ)0-thalassemia combined with β-thalassemia resulting in β-thalassemia major in China. Screening for δβ-thalassemia by Hb analysis could be an effective method.

The population incidence of thalassemia gene variants in Baise, Guangxi, P. R. China, based on random samples

OBJECTIVE

Thalassemia is a monogenic genetic disorder with a high prevalence in populations in the southern region of China. The thalassemia gene prevalence rate in the Baise population in China is high, and several rare gene variants have been detected in the population of this region during routine testing by our study group. To accurately reveal the thalassemia gene variants carried by the population in Baise, and to provide a basis for the formulation of thalassemia prevention and control policies in the region, we conducted a more comprehensive study in a randomly selected population.

RESULTS

In all, 4,800 randomized individuals were recruited for testing from Baise, and the detection of hot spot thalassemia genetic variants were performed by Gap-PCR and PCR-RDB methods, combined with the relative quantification of homologous fragments and AS-PCR to expand the detection range. The prevalence of thalassemia variants in this population was 24.19%, among which 16.69% of individuals carried α-thalassemia gene variants alone, 5.62% carried β-thalassemia gene variants alone, and 1.88% carried both variants.

CONCLUSIONS

The use of positive primary screening combined with hot spot gene variant detection alone can result in a certain degree of missed detection. In the prevention and control of thalassemia in the region, testing institutions need to pay attention to the detection of rare thalassemia gene variants such as ααα^anti4.2, ααα^anti3.7, -α^2.4, -α^21.9, β^-50, β^-90, and β^IVS-II-5, to provide more accurate genetic counseling advice to subjects.

Prime Editor 3 Mediated Beta-Thalassemia Mutations of the HBB Gene in Human Erythroid Progenitor Cells

Recently developed Prime Editor 3 (PE3) has been implemented to induce genome editing in various cell types but has not been proven in human hematopoietic stem and progenitor cells. Using PE3, we successfully installed the beta-thalassemia (beta-thal) mutations in the HBB gene in the erythroid progenitor cell line HUDEP-2. We inserted the mCherry reporter gene cassette into editing plasmids, each including the prime editing guide RNA (pegRNA) and nick sgRNA. The plasmids were electroporated into HUDEP-2 cells, and the PE3 modified cells were identified by mCherry expression and collected using fluorescence-activated cell sorting (FACS). Sanger sequencing of the positive cells confirmed that PE3 induced precise beta-thal mutations with editing ratios from 4.55 to 100%. Furthermore, an off-target analysis showed no unintentional edits occurred in the cells. The editing ratios and parameters of pegRNA and nick sgRNA were also analyzed and summarized and will contribute to enhanced PE3 design in future studies. The characterization of the HUDEP-2 beta-thal cells showed typical thalassemia phenotypes, involving ineffective erythropoiesis, abnormal erythroid differentiation, high apoptosis rate, defective alpha-globin colocalization, cell viability deterioration, and ROS resisting deficiency. These HUDEP-2 beta-thal cells could provide ideal models for future beta-thal gene therapy studies.

Identification of Two Novel Thalassemia Variants, HBA1: c.263delA and HBA2: c.376dupC, in Chinese Individuals

We detected a novel frameshift variant (HBA1: c.263delA) and - -^SEA (Southeast Asian), deletion in a 28-year-old Chinese woman with α-thalassemia (α-thal). This novel variant (a single nucleotide deletion at nucleotide 263 of codon 87) was detected by targeted next generation sequencing (NSG), resulting in a stop codon at amino acid 102 in exon 2 of the HBA1 gene. We also identified a novel heterozygous insertion (HBA2: c.376dupC) in a 24-year-old Chinese woman through screening for thalassemia. These two novel variants have expanded the mutation spectrum of α-thal and it would be beneficial for carrier screening, genetic counseling and prenatal diagnosis (PND) of α-thal.

A Novel β-Thalassemia Mutation [IVS-I-6 (T>G), HBB: c.92+6T>G] in a Chinese Family

β-Thalassemia (β-thal) is one of the most common inherited hemoglobin (Hb) disorders in southern China. Up to now, the mutation spectrum of β-thal has been increasingly broadened through various molecular methods. In this study, a 34-year-old female displaying microcytic, hypochromic anemia was first detected with a novel IVS-I-6 (T>G) (HBB: c.92+6T>G) mutation by Sanger sequencing. Pedigree analysis performed on her family showed that her mother and her daughter, who had abnormal hematological indices, also carried this mutation, while her other family members with normal hematological phenotypes, were not detected to carry any mutation. Based on the observed symptoms in this Chinese family, we concluded that this novel mutation was associated with a mild β-thal phenotype.

Detection of three common mutations causing β-thalassemia by using a closed-tube multiplex PCR

Small oligonucleotides mutations are the large majority causes of β-thalassemia. Dual priming oligonucleotide PCR has been used to detect point mutations and thus could be applied to diagnose β-thalassemia. The goal of this study was to establish a simple, quick and cost-effective screening assay by using modified dual priming oligonucleotide PCR for three most common mutations of β-thalassemia [CD71-72 (+A), CD 41-42 (-CTTT), Pnt.-28 (A → G)] in Southeast Asia and southern China. Man-made 5 tandem mismatched bases instead of poly (I) were used as the linker in the specific PCR primers. Single closed-tube multiplex PCRs followed by dissociation curve (DC) analysis were included in the molecular screening assay. Denaturing high-performance liquid chromatography analysis was applied to distinguish compound heterozygotes from single mutations. A blinded study of 91 samples was performed using this new assay. There were 41 samples detected as the above three mutations and it was concordant with the original methods. In conclusion, the modified dual priming oligonucleotide multiplex PCR/DC can detect these three genotypes of common mutation of β-thalassemia; this method is simple, rapid and cost-effective, which makes it suitable for large-scale screening and diagnosis.

Modified conditioning regimen improves outcomes of unrelated donor peripheral blood stem cell transplantation for β-thalassaemia major patients

BACKGROUND

The objective of this study was to evaluate the feasibility of a modified conditioning regimen for the treatment of patients with β-thalassaemia major (TM), using unrelated donor peripheral blood stem cell transplantation (UD-PBSCT).

METHODS

A modified conditioning regimen based on intravenous busulfan, cyclophosphamide, fludarabine, and antithymocyte globulin was performed in 50 consecutive childhood patients with β-TM and a median age of 4.6 years (range, 2-12 years). According to Pesaro's classification, three classes of risk are identified using the criteria of degree of hepatomegaly, portal fibrosis, and quality of the chelation treatment. Patients with three adverse criteria constituted class III, none of the adverse criteria constituted class I, and one or two of the adverse criteria formed class II. Ten patients were class I, 36 class II, and four class III. All patients were transplanted with UDs containing 37 of 10/10 human leukocyte antigen (HLA)-matched pairs, 11 of 9/10 matched pairs, and two of 8/10 matched pairs. The median follow-up was 36 months (range, 9-96 months).

RESULTS

All patients successfully achieved engraftment, two of whom developed persistent thrombocytopaenia. The incidence of acute graft-versus-host disease (aGVHD) grade III-IV and chronic graft-versus-host disease (cGVHD) were 12% and 8%, respectively. However, 8.3% of HLA-matched and 15.4% of HLA-mismatched patients developed aGVHD. The incidence of severe bacterial infections and fungal pneumonia was 12% and 20%, respectively. The 3-year overall survival, disease-free survival, graft rejection, and transplant-related mortality were 94%, 92%, 2%, and 6%, respectively.

CONCLUSION

This modified conditioning protocol effectively improved outcomes of UD-PBSCT for patients with β-TM.

Thalidomide has a significant effect in patients with thalassemia intermedia

OBJECTIVE

To investigate the effect of thalidomide in patients with thalassemia intermedia.

METHODS

We observed the effect of thalidomide in seven patients with thalassemia intermedia requiring blood transfusion. Four of the patients were transfusion-independent, and three patients were transfusion-dependent.

RESULTS

For the four transfusion-independent patients, hemoglobin concentration increased significantly (≥2 g/dl) in three and moderately (1-2 g/dl) in one. After 3 months of treatment, hemoglobin concentration increased 3.2 ± 1.2 g/dl compared to pretreatment. Among the three transfusion-dependent patients, transfusion was terminated after one month of treatment in one patient and decreased >50% in the other two patients, accompanied by an increase in the average hemoglobin concentration.

CONCLUSION

Thalidomide had a significant effect in patients with thalassemia intermedia. Further studies of a larger scale and more rigorous design are warranted.