A novel beta-thalassemia mutation [IVS-II-5 (G-->C)] in a Chinese family from Guangxi Province, P.R. China

The value of single-molecule real-time technology in the diagnosis of rare thalassemia variants and analysis of phenotype-genotype correlation

To compare single-molecule real-time technology (SMRT) and conventional genetic diagnostic technology of rare types of thalassemia mutations, and to analyze the molecular characteristics and phenotypes of rare thalassemia gene variants, we used 434 cases with positive hematology screening as the cohort, then used SMRT technology and conventional gene diagnosis technology [(Gap-PCR, multiple ligation probe amplification technology (MLPA), PCR-reverse dot blot (RDB)] for thalassemia gene screening. Among the 434 enrolled cases, conventional technology identified 318 patients with variants (73.27%) and 116 patients without variants (26.73%), SMRT identified 361 patients with variants (83.18%), and 73 patients without variants (16.82%). The positive detection rate of SMRT was 9.91% higher than conventional technology. Combination of the two methods identified 485 positive alleles among 49 types of variant. The genotypes of 354 cases were concordant between the two methods, while 80 cases were discordant. Among the 80 cases, 76 cases had variants only identified in SMRT method, 3 cases had variants only identified in conventional method, and 1 false positive result by the traditional PCR detection technology. Except the three variants in HS40 and HBG1-HBG2 loci, which was beyond the design of SMRT method in this study, all the other discordant variants identified by SMRT were validated by further Sanger sequencing or MLPA. The hematological phenotypic parameters of 80 discordant cases were also analyzed. SMRT technology increased the positive detection rate of thalassemia genes, and detected rare thalassemia cases with variable phenotypes, which had great significance for clinical thalassemia gene screening.

The Scope for Thalassemia Gene Therapy by Disruption of Aberrant Regulatory Elements

The common IVSI-110 (G>A) β-thalassemia mutation is a paradigm for intronic disease-causing mutations and their functional repair by non-homologous end joining-mediated disruption. Such mutation-specific repair by disruption of aberrant regulatory elements (DARE) is highly efficient, but to date, no systematic analysis has been performed to evaluate disease-causing mutations as therapeutic targets. Here, DARE was performed in highly characterized erythroid IVSI-110(G>A) transgenic cells and the disruption events were compared with published observations in primary CD34⁺ cells. DARE achieved the functional correction of β-globin expression equally through the removal of causative mutations and through the removal of context sequences, with disruption events and the restriction of indel events close to the cut site closely resembling those seen in primary cells. Correlation of DNA-, RNA-, and protein-level findings then allowed the extrapolation of findings to other mutations by in silico analyses for potential repair based on the clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated (Cas) 9, Cas12a, and transcription activator-like effector nuclease (TALEN) platforms. The high efficiency of DARE and unexpected freedom of target design render the approach potentially suitable for 14 known thalassemia mutations besides IVSI-110(G>A) and put it forward for several prominent mutations causing other inherited diseases. The application of DARE, therefore, has a wide scope for sustainable personalized advanced therapy medicinal product development for thalassemia and beyond.

A novel compound heterozygosity in Southern China: IVS-II-5 (G > C) and IVS-II-672 (A > C)

β-Thalassemia (β-thal) is a common hereditary anemia due to decreased or absent synthesis of the β-globin chains. Here, we report a patient found to be a novel compound heterozygote for the rare IVS-II-5 (G > C) (NG_000007.3: g.71044G > C) and IVS-II-672 (A > C) (NG_000007.3: g.71711A > C) mutations, which may be silent mutations that are associated with consistent residual output of β chains, normal red blood cell (RBC) indices and normal or borderline Hb A₂ levels.

Epidemiology of the delta globin alleles in southern Italy shows complex molecular, genetic, and phenotypic features

We characterized mutations and haplotypes of the delta-globin gene (HBD, MIM# 142000) in two regions of southern Italy. Mutations were discovered by screening for individuals with Hb A2<2%. In Basilicata, about 10,000 students were screened and 53 carriers in 43 unrelated families were diagnosed; in Campania, cases were referred through a routine thalassemia counseling service. Twelve alleles were detected. Four were novel variants [Hb A2-Metaponto (g.238C>A), Hb A2-Campania (g.302C>A), Hb A2-Lucania (g.393C>G), and Hb A2-Capri (g.443G>T)]. Hb A2-Lucania was not inherited but had arisen in the propositus. Two were novel mutations in the noncoding regions: the substitutions IVS2+6T>A, presumably affecting the splicing, and g.-126A>T in the GATA motif presumably affecting transcription. All novel alleles were found associated with haplotypes common in the Mediterranean area. The remaining six were alleles already described. The Hb A2-Yialousa (g.82G>T) was the most prevalent (42/63 families). Recurrent homologous crossing-over events have, most likely, linked this allele to Haplotypes IX (24 families), IV (10 families), or III (seven families). The ratio of Haplotypes IX:IV:III was about the same in the two regions. The rare allele Hb A2-NYU (g.39T>A) was found in 11 families from Basilicata associated with Haplotype I. All the 11 families lived in a restricted area extending from the Ionian Coast for 15 km along the Angri and Sinni Rivers. A founder effect most probably gave origin to this isolated group. The remaining four alleles were rare: the 7.2-kb deletion Corfù type (HBD g.-5946_1262del), Hb A2-Mitsero (g.14C>T), Hb A2-Etolia (g.385T>C), Hb A2-Coburg (g.1376G>A). Correlation between genotype and phenotype was established in 103 carriers.

The beta+-thalassemia mutation [IVS-II-5 (G-->C] creates an alternative splicing site in the second intervening sequence

We report a beta-thalassemia mutation [IVS-II-5 (G-->C)] in a Chinese family. Recently we cloned this beta-globin gene and studied its transient expression in murine erythroleukemia (MEL) cells. Both the thalassemic and normal beta-globin genes were isolated by polymerase chain reaction and TA-vector cloning. When the cloned beta-thalassemic globin gene was introduced into MEL cells, two kinds of spliced cytoplasmic beta-globin RNAs were detected. The predominant RNA was normally spliced, while the less abundant RNA contained an insertion of the first 47 nucleotides of the second intervening sequence localized between exons 2 and 3. These results suggest that the mutation [IVS-II-5 (G-->C)] causes a beta+-thalassemia.

A novel amber mutation in a beta zero-thalassaemia gene (beta 37TGG-->TAG), with direct detection by mapping the restriction fragments in amplified genomic DNA

A novel amber mutation, a G to A substitution at the second position of codon 37 in the beta-globin gene that changes the tryptophan coding triplet (TGG) to a termination codon (TAG), was found in a Chinese beta-thalassaemia carrier. The mutant gene creates an additional Dde I recognition site and eliminates the Ava II site, so this point mutation can be directly identified by restriction enzyme analysis.