Piero C. Giordano

Nine unknown rearrangements in 16p13.3 and 11p15.4 causing α- and β-thalassaemia characterised by high resolution multiplex ligation-dependent probe amplification

Background: Approximately 80% of the α- and 10% of the β-thalassaemias are caused by genomic deletions involving the α- and β-globin gene clusters on chromosomes 16p13.3 and 11p15.5, respectively. Gap-PCR, Southern blot analysis, and fluorescent in situ hybridisation are commonly used to identify these deletions; however, many deletions go undetected using conventional techniques. Methods: Patient samples for which no abnormalities had been found using conventional DNA techniques were analysed by a three colour multiplex ligation-dependent probe amplification assay. Two sets of 35 and 50 probes, covering a region of 700 kb of the α- and 500 kb of the β-globin gene cluster, respectively, were designed to detect rearrangements in the α- and β-globin gene clusters. Results: In 19 out of 38 patient samples, we found 11 different α-thalassaemia deletions, six of which were not previously described. Two novel deletions leaving the α-globin gene cluster intact were found to cause a complete downregulation of the downstream α-genes. Similarly, 31 out of 51 patient samples were found to carry 10 different deletions involving the β-globin gene cluster, three of which were not previously described. One involves the deletion of the locus control region leaving the β-globin gene cluster intact. Conclusions: These deletions, which are not easily detected by conventional techniques, may have clinical implications during pregnancy ranging from mild to life threatening microcytic haemolytic anaemia in neonates. The approach as described here is a rapid and sensitive method for high resolution analysis of the globin gene clusters and for any region of the genome.

The role of haemoglobin A2 testing in the diagnosis of thalassaemias and related haemoglobinopathies

The increase in haemoglobin (Hb)A2 level is the most significant parameter in the identification of β thalassaemia carriers. However, in some cases the level of HbA2 is not typically elevated and some difficulties may arise in making the diagnosis. For these reasons the quantification of HbA2 has to be performed with great accuracy and the results must be interpreted together with other haematological and biochemical evidence. The present document includes comments on the need for accuracy and standardisation, and on the interpretation of the HbA2 value, reviewing the most crucial aspects related to this test. A practical flow-chart is presented to summarise the significance of HbA2 estimation in different thalassaemia syndromes and related haemoglobinopathies.

Epidemiology of haemoglobin disorders in Europe: an overview

Objective. As a result of global population movements, haemoglobin disorders (thalassaemias and sickle cell disorders) are increasingly common in the formerly non‐indigenous countries of Northern and Western Europe and in the indigenous countries of Southern Europe. This article presents an overview of the changing picture and a method for assessing service needs. Method. Data on country of birth or ethnic origin of residents are adjusted to obtain the estimated proportions of residents and births in non‐indigenous groups at risk for haemoglobin disorders in European countries. The results are combined with prevalence data in each country of origin to obtain country prevalence estimates. Service indicators (annual tests or other interventions required to ensure equitable delivery of treatment and prevention) are then derived by country. Results. Haemoglobin disorders now occur at comparable frequency throughout Northern, Western and Southern Europe. Annually, there are more affected conceptions in Northern and Western than in Southern Europe, and sickle cell disorders are more common than thalassaemias. There is growing need for health policy‐makers to support motivated professionals working to develop optimal patient care, carrier diagnosis, genetic counselling and access to prenatal diagnosis throughout the Region. Conclusion. There is a strong case for pan‐European collaboration on haemoglobin disorders to share policies, standards and the instruments required to support them. These include methods for needs assessment, service standards, education and information strategies and materials, and methods for evaluating service delivery.

Unstable and Thalassemic α Chain Hemoglobin Variants: A Cause of Hb H Disease and Thalassemia Intermedia

We report an update of the α-globin gene point mutations resulting in structural modification associated with an α-thalassemia (α-thal) phenotype. These variants, barely symptomatic in the heterozygous state, are either unstable due to folding defects and/or defects in binding to α-hemoglobin stabilizing protein (AHSP). This is predicted to result in precipitation of the unstable α chains or Hb variant, a concomitant decrease in the overall quantity of normal α-globin in the red cells and a potential degree of anemia and possibly, hemolysis. Genotype/phenotype correlation and potential genetic risk in combination with common or less common α-thal defects are discussed.

ICSH recommendations for the measurement of Haemoglobin F

Although DNA analysis is needed for characterization of the mutations that cause β‐thalassaemia, measurement of the Hb A2 is essential for the routine identification of people who are carriers of β‐thalassaemia. The methods of quantitating Hb A2 are described together with pitfalls in undertaking these laboratory tests with particular emphasis on automated high‐performance liquid chromatography and capillary electrophoresis.

Segmental duplications involving the α-globin gene cluster are causing β-thalassemia intermedia phenotypes in β-thalassemia heterozygous patients

We describe two cases of simple heterozygosity for the common beta degrees -thalassemia mutation beta 39 (C-->T), both presenting with a thalassemia intermedia phenotype. In both cases synergic effect deriving from membrane defects or red cell enzyme deficiencies were excluded. In one case a triplication of the alpha-globin genes was found which did not justify the severity of the transfusion-dependent phenotype. Multiplex ligation-dependent probe amplification (MLPA) analysis of the alpha-globin gene cluster revealed two new rearrangements, consisting of a full duplication of the alpha-globin genes locus including the upstream regulatory element. In one case the duplication was in the presence of the common anti-alpha(3.7) triplication in trans, resulting in a total of 7 active alpha-globin genes. In the other case the duplicated allele and the normal allele in trans resulted into a total of 6 active alpha-globin genes. We report the clinical and hematological data and the molecular analysis and discuss the occurrence of alpha-globin genes duplication defects in cases of beta-thalassemia heterozygotes with thalassemia intermedia phenotypes.

Rapid detection of point mutations and polymorphisms of the α-globin genes by DGGE and SSCA

We report the application of DGGE and SSCA for the identification of point mutations causing α‐thalassemia. The α‐globin genes were amplified in three overlapping fragments of 250 bp (I), 540 bp (II), and 600 bp (III), respectively. Fragments II and III were analyzed by DGGE, while fragments I and II were analysed by SSCA. A panel of seven previously identified mutations was employed to test the combined DGGE/SSCA strategy: 5/5 and 6/7 mutations were detected by SSCA and DGGE, respectively. The same approach has also led to the identification of eight disease‐causing mutations in a sample of 18 presumed non‐deletional α‐thalassemia carriers. During this pilot study, two novel mutations as well as three new polymorphisms were found. The combined application of SSCA and DGGE allows the rapid identification of mutations responsable for α‐thalassemia and abnormal globin chain variants. Moreover, it will prove extremely useful for pre‐ and postnatal diagnosis and in screening programs for non‐deletional α‐thalassemias.

The involvement of Alu repeats in recombination events at the α-globin gene cluster: characterization of two α°-thalassaemia deletion breakpoints

Abstract Alu repetitive sequences are frequently involved in homologous and non-homologous recombination events in the α-cluster. Possible mechanisms involved in Alu-mediated recombination events are strand exchange, promoted by DNA pairing between highly homologous Alu repeats, and subsequent strand invasion. Alternatively, Alu sequences might play a more active role in recombinogenic processes in the α-cluster. We describe a novel 33-kb α°-thalassaemia deletion ––DUTCH encompassing the α- and zeta-globin genes and pseudogenes in a kindred of Dutch-Caucasian origin. This deletion appears similar, although not identical, to the previously described ––MEDII deletion. Cloning and sequencing of both the ––DUTCH and ––MEDII deletion breakpoints clearly indicate that the mechanism leading to these α°-thalassaemia deletions involves misalignment between the highly homologous tandemly arranged Alu repeats at both parental sides, which are normally 33 kb apart. Comparison of breakpoint positions along the Alu consensus sequence indicate the involvement of a 26-bp core sequence in two out of five α°-thalassaemia deletions. This sequence has been identified by others as a possible hotspot of recombination. These findings favour the idea that Alu repeats stimulate recombination events not only by homologous pairing, but also by providing binding sites for recombinogenic proteins.

β-THALASSEMIA INTERMEDIA FROM SOUTHERN IRAN: IVS-II-1 (G→A) IS THE PREVALENT THALASSEMIA INTERMEDIA ALLELE

The preliminary results of a pilot study are reported, intended as an initiation of a research plan, focused on the prevention of β-thalassemia in Iran. The aims of this study are: (i) to improve the knowledge of the molecular background of β-thalassemia intermedia in Southern Iran; (ii) to verify the role of the −158 Gγ (C→T) (Xmn I) polymorphism as a modulating factor in thalassemia intermedia; (iii) to test the validity of the multiplex and single mutation specific amplification refractory mutation system in analyzing the molecular defects causing β-thalassemia in multiethnic populations; and (iv) to develop suitable strategies for the application of prevention protocols in Iran. To accomplish the task we have selected 87 β-thalassemia intermedia patients and adapted the DNA methodology to detect the following 11 frequent mutations in Iran: codon 5 (−CT); frameshift codons (FSC) 8/9 (+G); codon 30 (G→C); IVS-I-1 (G→A); IVS-I-5 (G→C); IVS-I-6 (T→C); IVS-I-110 (G→A); codons 36/37 (−T); codon 44 (−C); IVS-II-1 (G→A); IVS-II-745 (C→G). Because of the multiethnicity of the population we have also included the Indian IVS-I (25 bp deletion) and the Mediterranean IVS-I-130 (G→C) and codon 39 (C→T) mutations. Forty-eight patients were randomly studied for the Xmn I polymorphism together with 50 healthy volunteers as a control group. The molecular analysis conducted in Iran, identified only 31% of the alleles that were presumed to be thalassemic, revealing either a strategic or a technical insufficiency of the chosen method. However, the mutations with the highest prevalence in the country (IVS-II-1, IVS-I-110, IVS-I-1 and FSC 8/9) were found. As expected the IVS-II-1 defect, being the most frequent in south Iran, was present at the highest rate (24%). The Xmn I polymorphism was found in association with this prevalent mutation and was detected in the homozygous state in 87.5% of the patients homozygous for the IVS-II-1 (G→A) mutation. The overall positivity for Xmn I was found in 40.6% of the thalassemic alleles vs. 14% in the non-thalassemic, confirming the hypothesis of an older event, antecedent to the IVS-II-1 mutation. In trying to assess a more suitable molecular detection method we intend to continue this study in collaboration with the European centers involved, applying more effective technologies and better defining the molecular spectrum of β-thalassemia in the sub-populations. We also intend to verify the effect of α-thalassemia in the genotype/phenotype correlation of β-thalassemia intermedia.

Variation of CNV distribution in five different ethnic populations

Recent studies have revealed a new type of variation in the human genome encompassing relatively large genomic segments (∼100 kb–2.5 Mb), commonly referred to as copy number variation (CNV). The full nature and extent of CNV and its frequency in different ethnic populations is still largely unknown. In this study we surveyed a set of 12 CNVs previously detected by array-CGH. More than 300 individuals from five different ethnic populations, including three distinct European, one Asian and one African population, were tested for the occurrence of CNV using multiplex ligation-dependent probe amplification (MLPA). Seven of these loci indeed showed CNV, i.e., showed copy numbers that deviated from the population median. More precise estimations of the actual genomic copy numbers for (part of) the NSF gene locus, revealed copy numbers ranging from two to at least seven. Additionally, significant inter-population differences in the distribution of these copy numbers were observed. These data suggest that insight into absolute DNA copy numbers for loci exhibiting CNV is required to determine their potential contribution to normal phenotypic variation and, in addition, disease susceptibility.