A novel beta-delta globin gene fusion, anti-Lepore Hong Kong, leads to overexpression of delta globin chain and a mild thalassaemia intermedia phenotype when co-inherited with beta(0)-thalassaemia

Abnormal hemoglobin anti-Lepore Hong Kong compound with β0-thalassemia ameliorate thalassemia severity when co-inherited with α-thalassemia

Abnormal hemoglobin anti-Lepore Hong Kong is a rare βδ fusion variants resulting from non-homologous crossover during meiosis. Anti-Lepore Hong Kong is known to consistently exhibit significantly increased level of HbA2. In this study, we used multiplex ligation-dependent probe amplification (MLPA) and single molecular real-time (SMRT) sequencing, as well as Sanger sequencing, to identify variants in five unrelated families with abnormal elevated HbA2 level. All probands in these five families were found to be heterozygous for anti-Lepore Hong Kong. Among them, two families showed co-occurrence of β0-thalassemia and α-thalassemia (-SEA/ or αCSα/). Heterozygotes for anti-Lepore Hong Kong displayed an average HbA2 level of 17.7% and behaved normal. However, when combined with β0-thalassemia and α-thalassemia, the probands exhibited higher HbA2 level (30.2-40.8%) and behaved with β-thalassemia trait. Furthermore, determination of the α/β-mRNA ratio revealed a slight downregulation of β-globin, similar to that of β-thalassemia minor. Our study is the first to identify compound heterozygotes for anti-Lepore Hong Kong, β0-thalassemia and α-thalassemia, provide valuable information for prenatal counseling.

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.

Hb Lepore-Hong Kong: First Report of a Novel δ/β-Globin Gene Fusion in a Chinese Family

We describe a new δ/β fusion gene causing β-thalassemia (β-thal) trait and its formation mechanism. The proband was a 39-year-old woman who presented with persistent microcytic microcytosis without iron deficiency. Molecular diagnoses revealed a δβ configuration within a 54 bp region between the Cap site (+22) and codon 8, causing a deletion (NG_000007.3: g.63154_70565del). This results in a variant that has been named Hb Lepore-Hong Kong and shows a decreased β-globin mRNA in carriers compared to that of normal subjects. It is assumed that combination of this variant with β-thal may cause severe β-thal syndrome.

Diverse hematological phenotypes of β-thalassemia carriers

Most β-thalassemia carriers have mild anemia, low mean corpuscular volume and mean corpuscular hemoglobin, and elevated hemoglobin α2 (HbA2 ). However, there is considerable variability resulting from coinheritance with α- and/or δ-globin gene mutations, dominant inheritance of β-thalassemia mutations, highly unstable variant globin chains, large deletions removing part or all of the β-globin gene cluster, loss of heterozygosity of the β-globin gene cluster during development, or concomitant erythroid enzyme or membrane protein abnormalities. Recognition of the specific abnormality and correct diagnosis can allay anxiety and unnecessary investigation, help formulate treatment programs, and deliver appropriate genetic and family counseling.

Diagnosis and prevention of thalassemia

Thalassemia is the most common monogenic inherited disease worldwide and it affects most countries to various extents. This review summarizes the current approaches to phenotypic and genotypic diagnosis of thalassemia in clinical practice. Prevention strategies that encompass carrier screening, genetic counseling and prenatal diagnosis are discussed. The importance of public education and an awareness of a changing perception regarding this group of diseases are emphasized. It also addresses the impact of the rapidly increasing knowledge in disease severity modification by hemoglobin F (Hb F).

Detection of a novel βδ-globin fusion gene, anti-lepore Hb CHORI (β(through IVS-I-57)/δ(from IVS-I-101)), by multiplex ligation-dependent probe amplification

Anti-Lepore hemoglobins (Hbs) are rare βδ fusion variants that arise from non homologous crossover during meiosis. Using multiplex ligation-dependent probe amplification (MLPA), we identified a novel anti-Lepore Hb in an individual with an ambiguous Hb variant detected on routine screening by electrophoresis and high performance liquid chromatography (HPLC). The results of MLPA revealed duplication of β and δ gene segments. Resolution of the rearrangement by DNA sequencing confirmed a novel anti-Lepore Hb, molecularly distinct from Hb P-Nilotic, which we have named anti-Lepore Hb CHORI (Children's Hospital Oakland Research Institute) (β(through IVS-I-57)/δ(from IVS-I-101)).

Hb Iberia [α104(G11)Cys → Arg,TGC>CGC (α2) (HBA2:c.313T>C)], a new α-thalassemic hemoglobin variant found in the Iberian Peninsula: report of six cases

We report a new structural defect of the α2-globin chain presenting with moderate microcytic hypochromic anemia, in six individuals from three unrelated families, living in Portugal and Spain. α-Globin gene deletions were ruled out by gap-polymerase chain reaction (gap-PCR) and multiplex ligation-dependent probe amplification (MLPA). Direct sequencing of the α2-globin gene revealed a substitution of codon 104 [α104(G11)Cys→Arg, TGC>CGC (α2) (HBA2:c.313T>C)]. This new variant, not detectable by high performance liquid chromatography (HPLC) or electrophoresis, was called Hb Iberia, as it was observed for the first time in families from the Iberian Peninsula. Although the mutant allele is transcribed, as indicated by the balanced mRNA α/β ratio, the abnormal α2 chain could not form a stable tetramer as the cysteine and arginine residues, located at the α1β1 contact, differ in size, charge and hydrophobicity. Hb Iberia is the third mutation described at codon 104 on the α-globin genes, namely, Hb Sallanches (α2, TGC>TAC) and Hb Oegstgeest (α1, TGC>AGC), also characterized as unstable hemoglobins (Hbs), present on an α-thalassemic phenotype.

Hb Charlieu [alpha106(G13)Leu-->Pro (alpha1)]: a new phenotypically silent hemoglobin variant associated with a mild alpha-thalassemia phenotype

A chronic microcytosis and hypochromia without any iron deficiency were observed in an 11-year-old boy of French Caucasian origin. The same hematological findings were also found for his mother. No abnormal hemoglobin (Hb) was detected using isoelectric focusing, cation exchange liquid chromatography and reversed phase liquid chromatography of the globin chains but DNA sequencing revealed a CTG>CCG transition at codon 106 (Leu-->Pro) of the alpha1-globin gene in both of them. As the alpha/beta mRNA ratios, determined by reverse-transcriptase real-time quantitative polymerase chain reaction (PCR), are not concordant with an alpha-thalassemia (alpha-thal) state, we hypothesize that the underlying physiopathologic mechanism is an assembling defect of the Hb Charlieu molecule, rather than an instability of the alpha(Charlieu) mRNA. Moreover, genetic counseling and patient information are required in this family to prevent potentially severe alpha-thalassemias in following generations.

The expanding spectrum of thalassemia intermedia

The hemoglobin disorders serve as a model for study of the genetic heterogeneity underlying the phenotype of genetic disorders. 'Thalassemia intermedia' is a clinical phenotype which displays marked genotypic variability in different populations or ethnic groups. Two common underlying mechanisms include co-inheritance of alpha globin gene deletions in homozygous thalassemia intermedia and presence of XmnI polymorphism. The newly described mechanisms including unstable hemoglobin disorders and somatic deletions in beta-globin gene are elaborated in the present review.

The significance of the hemoglobin A(2) value in screening for hemoglobinopathies

BACKGROUND AND OBJECTIVE

The inherited hemoglobinopathies are a large group of disorders that include thalassemias and hemoglobin variants. Accurate determination of the carrier phenotype is essential for detecting couples at risk for producing offspring with hemoglobinopathy. Heterozygous beta-thalassemia is usually silent at the clinical level. His phenotype is characterized by microcytosis and hypochromia with increased hemoglobin A(2) (HbA(2)) value. Therefore, HbA(2) determination plays a key role in screening programs for hemoglobinopathy. The aim of this review is to address and suggest an approach for reducing or abolishing hemoglobinopathy screening mistakes.

DESIGN AND METHODS

Quantitative methods for HbA(2) value determination, comment on the accuracy of the test and on the interpretation of data were discussed. The most probable diagnostic conclusion based on the HbA(2) level, hemoglobin pattern, hematological parameters and iron markers was suggested in this review.

RESULTS

Hemoglobinopathies are the only genetic disease where it is possible to detect carriers using hematological findings rather than DNA analysis. However, hematological diagnosis is sometimes presumptive, and in these cases, DNA analysis becomes necessary. Complete screening is based on the detection of red cell indices, HbA(2), HbF and hemoglobin variant values. In particular, HbA(2) determination plays a key role in screening programs for beta-thalassemia because a small increase in this fraction is one of the most important markers of beta-thalassemia heterozygous carriers.

CONCLUSION

Genetic factors both related and unrelated to the beta- and alpha-globin gene clusters, iron metabolism, endocrinological disorders, and some types of anemia, together with intra- and inter-laboratory variations in HbA(2) determination, may cause difficulties in evaluating this measurement in screening programs for hemoglobinopathies. Therefore, knowledge of all these issues is important for reducing or eliminating the risk of mistakes in screening programs for hemoglobinopathies.

Hereditary pancreatitis caused by a double gain-of-function trypsinogen mutation

Hereditary pancreatitis, an autosomal dominant disease with approximately 80% penetrance, can be caused by both 'gain-of-function' missense and copy number mutations in the cationic trypsinogen gene (PRSS1). Here we demonstrate a heterozygous hybrid PRSS2 (encoding anionic trypsinogen)/PRSS1 gene in a French white family with hereditary pancreatitis, by means of quantitative fluorescent multiplex PCR and RT-PCR analyses. The hybrid gene, in which exons 1 and 2 are derived from PRSS2 and exons 3-5 from PRSS1, apparently resulted from a non-allelic homologous recombination (NAHR) event between the chromosome 7 homologs or sister chromatids during meiosis. Interestingly, this hybrid gene causes the disease through a combination of its inherent 'double gain-of-function' effect, acting simultaneously as a 'quantitative' copy number mutation and a 'qualitative' missense mutation (i.e. the known disease-causing p.N29I mutation). Our finding reveals a previously unknown mechanism causing human inherited disease, enriches the lexicon of human genetic variation and goes beyond the known interaction between copy number variations (CNVs) and single nucleotide substitutions in health and disease. Our finding should also stimulate more interest in analyzing both types of genetic variation whenever one tries to determine the contribution of a specific locus to a given disease phenotype.