Here, we report a novel frameshift mutation caused by a single base deletion in exon 3 of the HBA2 gene (HBA2:c.337delC) detected by next-generation sequencing. The proband was a 26-year-old Chinese pregnant woman who originates from Hunan Province. Her mean corpuscular volume(MCV) and mean corpuscular hemoglobin (MCH) had a mild decrease. Capillary electrophoresis (CE) showed that both Hb A (97.8%) and Hb F (0.0%) values were within normal range, while the Hb A2 (2.2%) value was below normal. Sequence analysis of the α and β-globin genes revealed a novel single base deletion at codon 112 (HBA2:c.337delC) in the heterozygous state, which resulted in a mild phenotype of α-thalassemia.

Thalassemia is a genetic blood disorder characterized by decreased hemoglobin production. Severe anemia can damage organs and severe threat to life safety. Allogeneic transplantation of bone marrow-derived hematopoietic stem cell (HSCs) at present represents a promising therapeutic approach for thalassemia. However, immune rejection and lack of HLA-matched donors limited its clinical application. In recent years, human-induced pluripotent stem cells (hiPSCs) technology offers prospects for autologous cell-based therapy since it could avoid the immunological problems mentioned above.
In the present study, we established a new hiPSCs line derived from amniotic cells of a fetus with a homozygous β41-42 (TCTT) deletion mutation in the HBB gene and a heterozygous Westmead mutation (C > G) in the HBA2 gene. We designed a CRISPR-Cas9 to target these casual mutations and corrected them. Gene-corrected off-target analysis was performed by whole-exome capture sequencing. The corrected hiPSCs were analyzed by teratoma formation and erythroblasts differentiation assays.
These mutations were corrected with linearized donor DNA through CRISPR/Cas9-mediated homology-directed repair. Corrections of hiPSCs were validated by sequences. The corrected hiPSCs retain normal pluripotency. Moreover, they could be differentiated into hematopoietic progenitors, which proves that they maintain the multilineage differentiation potential.
We designed sgRNAs and demonstrated that these sgRNAs facilitating the CRISPR-Cas9 genomic editing system could be applied to correct concurrent α- and β-thalassemia in patient-derived hiPSCs. In the future, these corrected hiPSCs can be applied for autologous transplantation in patients with concurrent α- and β-thalassemia.

We report a rare mutation, HBA2: c.184A>T on the α2-globin gene, detected in a Chinese proband who presented with Hb H disease and a mild anemia. This frameshift mutation results in a premature termination of translation at position 61 of the α2-globin gene. Carriers of this mutation showed a borderline microcytic hypochromia. Our study indicates the importance of screening nondeletional α-thalassemia (α-thal) in areas with a particularly high prevalence of thalassemia such as in Southern China, especially for couples with one partner carrying an α0-thal deletion.

BACKGROUND: Elevated HbA2 (hemoglobin A2) level is considered the most reliable hematological parameter for the detection of β-thalassemia carriers. However, some carriers are difficult to recognize because the level of HbA2 is not in the distinctive carrier range, i.e. 4.0-6.0%; instead, some carriers have HbA2 levels between normal and carrier levels, i.e. borderline HbA2 (HbA2 = 3.1-3.9%). Studies have shown that variations in the erythroid Krüppel-like factor (KLF1) gene lead to borderline HbA2 in β-thalassemia carriers from various populations. The incidence of borderline HbA2 in Saudis is high.
METHODS: To confirm the influence of variations in KLF1, HBA1, HBA2 and HBB genes for the reduction of the level of HbA2 in Saudi β-thalassemia carriers, we performed a direct sequence analysis of KLF1, HBA1, HBA2 and HBB genes from 212 healthy Saudis (88 subjects: HbA2 < 3; 72 subjects: HbA2 = 3.1 to 3.9; 52 subjects HbA2 > 4.3).
RESULTS: The presence of the borderline HbA2 level is not specific to any type of β-thalassemia variation or β+-thalassemia variations in Saudis. Two exonic (c.304T>C and c.544T>C) and two 3\' untranslated region (3\'UTR) (c.*296G>A and c.*277C>G) variations have been identified in the KLF1 gene for the first time from an Arab population. None of these four variations in KLF1 genes are significantly associated with the Saudis with borderline HbA2. α Globin genotype, -α23.7/α1α2, is found to be the most frequent (55.55%) among healthy Saudis with borderline HbA2 compared with the other groups (HbA2 < 3 = 20.45%; HbA2 > 4.3 = 13.51%).
CONCLUSIONS: Further studies are necessary to determine the influence of other factors on the presence of borderline HbA2 in 41.67% of Saudis.

Multiple imputation based on chained equations (MICE) is an alternative missing genotype method that can use genetic and nongenetic auxiliary data to inform the imputation process. Previously, MICE was successfully tested on strongly linked genetic data. We have now tested it on data of the HBA2 gene which, by the experimental design used in a malaria association study in Tanzania, shows a high missing data percentage and is weakly linked with the remaining genetic markers in the data set. We constructed different imputation models and studied their performance under different missing data conditions. Overall, MICE failed to accurately predict the true genotypes. However, using the best imputation model for the data, we obtained unbiased estimates for the genetic effects, and association signals of the HBA2 gene on malaria positivity. When the whole data set was analyzed with the same imputation model, the association signal increased from 0.80 to 2.70 before and after imputation, respectively. Conversely, postimputation estimates for the genetic effects remained the same in relation to the complete case analysis but showed increased precision. We argue that these postimputation estimates are reasonably unbiased, as a result of a good study design based on matching key socio-environmental factors.