Carlos D. De Brasi

Analysis of factor VIII gene intron 1 inversion in Argentinian families with severe haemophilia A and a review of the literature.

Besides intron 22 factor VIII gene inversion (Inv22), intron 1 inversion (Inv1) has recently been reported as a further recurrent mutation that causes approximately 5% of severe haemophilia A (HA) cases. We analysed the presence of the Inv1 in a group of 64 severe HA-affected families from Argentina, and found only one positive case. This Inv1 patient has not developed a factor VIII inhibitor, and the screening for small mutations in the coding sequences of the factor VIII gene did not detect any additional defect in this case. The Inv1 genotyping was further applied to analyse the haemophilia carrier status of the probands sister. In addition, we studied the accuracy of the current polymerase chain reaction-based method to investigate the Inv1, and confirmed the absence of amplimer length polymorphisms associated to the Inv1-specific polymerase chain reaction amplifications in 101 X-chromosome haplotypes from unrelated Argentinian healthy males. In order to discuss Inv1 mutation frequency in severe HA and the risk of inhibitor formation, a review of the literature was included. Our data highlight the importance of analysis of the Inv1 in Inv22-negative severe HA cases. This will benefit both genetic counselling and the study of the relationship between genotype and inhibitor development.

Symptomatic female carriers of Duchenne muscular dystrophy (DMD): Genetic and clinical characterization

Duchenne muscular dystrophy (DMD) is an X-linked recessive disease caused by mutations in the dystrophin gene and is characterized by muscle degeneration and death. DMD affects males; females being asymptomatic carriers of mutations. However, some of them manifest symptoms due to a translocation between X chromosome and an autosome or to a heterozygous mutation leading to inactivation of most of their normal X chromosome. Six symptomatic female carriers and two asymptomatic were analyzed by: I) Segregation of STRs-(CA)n and MLPA assays to detect a hemizygous alteration, and II) X chromosome inactivation pattern to uncover the reason for symptoms in these females. The symptomatic females shared mild but progressive muscular weakness and increased serum creatin kinase (CK) levels. Levels of dystrophin protein were below normal or absent in many fibers. Segregation of STRs-(CA)n revealed hemizygous patterns in three patients, which were confirmed by MLPA. In addition, this analysis showed a duplication in another patient. X chromosome inactivation assay revealed a skewed X inactivation pattern in the symptomatic females and a random inactivation pattern in the asymptomatic ones. Our results support the hypothesis that the DMD phenotype in female carriers of a dystrophin mutation has a direct correlation with a skewed X-chromosome inactivation pattern.

Eighteen Years of Molecular Genotyping the Hemophilia Inversion Hotspot: From Southern Blot to Inverse Shifting-PCR

The factor VIII gene (F8) intron 22 inversion (Inv22) is a paradigmatic duplicon-mediated rearrangement, found in about one half of patients with severe hemophilia A worldwide. The identification of this prevalent cause of hemophilia was delayed for nine years after the F8 characterization in 1984. The aim of this review is to present the wide diversity of practical approaches that have been developed for genotyping the Inv22 (and related int22h rearrangements) since discovery in 1993. The sequence— Southern blot, long distance-PCR and inverse shifting-PCR—for Inv22 genotyping is an interesting example of scientific ingenuity and evolution in order to resolve challenging molecular diagnostic problems.

A new polymorphism in the human factor VIII gene: implications for linkage analysis in haemophilia A and for the evolution of int22h sequences

A new polymorphism in the human factor VIII gene has been localized and characterized. It is a biallelic, single nucleotide polymorphism located in intron 22 of the gene, within the 9·5 kb int22h‐1 segment. The allelic forms are G (frequency 0·65) and A (frequency 0·35), giving a predicted rate of heterozygosity of 0·46. The polymorphism occurs within a CG dinucleotide and affects an MspI site (CCGG). Int22h‐1 is duplicated twice extragenically at Xq28; both extragenic copies (int22h‐2 and ‐3) are also polymorphic with respect to MspI. Investigation of 156 MspI [–] alleles, comprising 30 intragenic and 126 extragenic sites, indicated that all were due to A alleles and none had arisen by C to T transition within the CG dinucleotide. The intragenic MspI site (designated MspI A) is located 737 bases downstream of a previously described XbaI restriction fragment length polymorphism. Despite their close proximity, the polymorphisms are not in complete linkage disequilibrium; haplotype analysis in 85 factor VIII genes from a Caucasian population predicts an informativity of approximately 60% in linkage studies using both, compared with an informativity of approximately 47% in studies using either on its own.

Novel mutational mechanism in the thyroglobulin gene: Imperfect DNA inversion as a cause for hereditary hypothyroidism

The objective of this study was to perform genetic analysis in three brothers of Turkish origin born from consanguineus parents and affected by congenital hypothyroidism, goiter and low levels of serum TG. The combination of sequencing of DNA, PCR mapping, quantitative real-time PCR, inverse-PCR (I-PCR), multiplex PCR and bioinformatics analysis were used in order to detect TG mutations. We demonstrated that the three affected siblings are homozygous for a DNA inversion of 16,962bp in the TG gene associated with two deleted regions at both sides of the inversion limits. The inversion region includes the first 9bp of exon 48, 1015bp of intron 47, 191bp of exon 47, 1523bp of intron 46, 135bp of exon 46 and the last 14,089bp of intron 45. The proximal deletion corresponds to 27bp of TG intron 45, while the distal deletion spans the last 230bp of TG exon 48 and the first 588bp of intergenic region downstream TG end. The parents were heterozygous carriers of the complex rearrangement. In conclusion, a novel large imperfect DNA inversion within the TG gene was identified by the strategy of I-PCR. This aberration was not detectable by normal sequencing of the exons and exon/intron boundaries. Remarkably, the finding represents the first description of a TG deficiency disease caused by a DNA inversion.

Specific assessment of BCR–ABL transcript overexpression and imatinib resistance in chronic myeloid leukemia patients

Imatinib mesylate has proven to be the most effective treatment in chronic myeloid leukemia. Nevertheless, imatinib resistance has raised concern and prompted interest in additional strategies to achieve disease eradication. Resistance to imatinib is mainly associated with three mechanisms: acquired mutations in the kinase domain of BCR–ABL protein, genetic amplification, and transcript overexpression of BCR–ABL rearrangement. Therefore an accurate assessment of resistance mechanism is particularly important to improve strategies to overcome resistance. In order to determine overexpression of BCR–ABL, we propose a method that correlates quantitative real time PCR and fluorescence in situ hybridization data from the same peripheral blood sample. The ratio between both methodologies permits to calculate the expression index (EI) for each patient. EI estimates the rate of BCR–ABL transcription per rearrangement. The median EI value, including all cases (n = 123), was 0.288; those cases (n = 13) included in percentile 90 showed an increment of EI above 1 Log (>2.88) with respect to the median value and were considered as cases with overexpression. We also evaluated the EIs using receiver operating characteristics curve; choosing an EI cutoff of 1.836 we obtained a sensitivity of 95% and a specificity of 61%. Using this EI cutoff value, more patients (n = 17) were included in the overexpression group. Patients within this group were resistant to imatinib and also showed a worse overall survival if compared with the remaining.

Specific analysis of the intron 22 XbaI polymorphism of the human factor VIII gene using long-distance PCR.

A rapid, non‐radioactive, PCR‐based method to genotype the XbaI restriction fragment length polymorphism of the human factor VIII gene is described. The method uses long‐distance PCR followed by XbaI restriction digestion and agarose gel electrophoresis. The 6.6 kb amplification product includes a constant XbaI site, which provides a digestion control. The specificity of the method was challenged by a blind experiment with 16 genomic DNA samples previously genotyped by Southern blot analysis: a perfect correlation was obtained between genotypes determined using Southern blot and PCR.

Are int22h-mediated deletions a common cause of hemophilia?

Dear Editor, Hemophilia A (HA) (OMIM 306700) is an X-linked inherited bleeding disorder caused by deleterious mutations in the coagulation factor VIII gene (F8). Even though there is a broad diversity of HA-causative mutations, an uncommon type of rearrangement—a large DNA inversion involving F8 intron 22 (Inv22)—accounts for approximately one half of severely affected patients. Inv22 was formerly described by Lakich et al. [1] and Naylor et al. [2]. A collaborative international effort estimated that Inv22 is the cause of 43% (35%, 7%, and 1% for Inv22 type I, type II, and rare types, respectively) of severe HA cases worldwide with minor geographical or ethnical differences [3], in close agreement with our corresponding Argentinean series (42% of Inv22, and 34% and 7% for type I and type II, respectively) [4]. Naylor et al. [5] indicated that Inv22 originates by homologous recombination between well-defined duplicons (int22h) of 9.5 kb located one copy within F8 intron 22 (int22h-1, h1) and the other, inversely oriented, from a group of two extragenic copies (int22h-3, h3 for Inv22 type I and int22h-2, h2 for type II). It was formerly believed that h2 and h3 were equally oriented (i.e., head to tail). However, Ross et al. [6] determined that h2 and h3 are inversely oriented (i.e., head to head), both embedded in the arms of a large imperfect palindrome (Fig. 1). This finding prompted Bagnall et al. [7] to hypothesize recombination between these arms interchanging the location of the extragenic int22h copies and generating a non-deleterious inversion polymorphism in Xq28, i.e., h123 and h132. In this scenario, Inv22 type I may be generated from intrachromosomal recombination between h1 and h3 on the most frequent variant h123 whereas Inv22 type II may be generated between h1 and h2 on the least frequent h132 (Fig. 1). Moreover, on each of these normal structural variants of the X chromosome, recombination between h1 with either equally oriented copies (h2 or h3) may generate deletions (Del22) or duplications (Dup22) but not inversions [7]. More precisely, Del22 type I would be generated by recombination between h1 and h3 on variant h132 whereas Del22 type II by recombination between h1 and h2 on variant h123 [8] (Fig. 1). Notwithstanding these theoretical speculations, until recently, no such Del22 mutation has been unequivocally reported in the literature, and Del22 has been suspected to be extremely deleterious, even to compromise the viability of hemizygous males [8]. Unexpectedly, a recent paper by Abou-Elew et al. [9] detected three cases of Del22 (two Del22 type II and one type I) by the use of inverse-shifting PCR (IS-PCR) [10] in a group of 13 Egyptian patients with severe HA. In this scenario and previous beliefs on the phenotype of int22h-mediated deletions (Del22), the aims of this scientific letter are, first, to report the lack of Del22 in a series of int22h-mediated rearrangements from Argentina and, second, to provide a simple practical approach to Electronic supplementary material The online version of this article (doi:10.1007/s00277-011-1295-z) contains supplementary material, which is available to authorized users. M. M. Abelleyro : L. C. Rossetti : C. P. Radic : I. B. Larripa : C. D. De Brasi (*) Departamento de Genetica, Instituto de Investigaciones Hematologicas, Academia Nacional de Medicina de Buenos Aires, Pacheco de Melo 3081, Buenos Aires 1425, Argentina e-mail: cdebrasi@hematologia.anm.edu.ar

BAX/BCL-XL gene expression ratio inversely correlates with disease progression in chronic myeloid leukemia.

BCR-ABL fusion gene is implicated in the pathogenesis of chronic myeloid leukemia (CML), encoding the oncoprotein p210(BCR-ABL) with anti-apoptotic activity. The inability to undergo apoptosis is an important mechanism of drug resistance and neoplastic evolution in CML. The gene transcript expression of mitochondrial apoptotic related genes BAX and BCL-XL was evaluated by quantitative Real Time PCR (qPCR) in vitro in K562 cells and in vivo in peripheral blood of 66 CML patients in different stages of the disease: 13 cases at diagnosis, 34 in chronic phase (CP), 10 in accelerated phase (AP) and 9 in blast crisis (BC). Our results in K562 cells showed that all treatments with different tyrosine kinase inhibitors (TKIs) induced a decreased expression of the antiapoptotic oncogene BCL-XL, whereas the proapoptotic gene BAX remains constant with minor modifications. A significantly lower BAX/BCL-XL expression ratio (mean±SEM) than a group of healthy individuals (4.8±0.59) were observed in CML patients at diagnosis (1.28 ± 0.16), in AP (1.14±0.20), in BC (1.16±0.30) and in 18% of cases of patients in CP (2.71±0.40). Most CP cases (82%) showed a significantly increased ratio (10.03±1.30), indicating that the treatment with TKIs efficiently inhibited the expression of BCL-XL by blocking BCR-ABL oncoprotein. The BAX/BCL-XL ratio showed a significant inverse correlation (Spearman P<0.0001) with BCR-ABL/ABL relative expression indicating that low BAX/BCL-XL was associated with disease progression. Accordingly, the follow up of a cohort of eight cases during 6months from diagnosis showed that while the BAX/BCL-XL ratio rapidly increased after treatment in seven cases with good evolution, it decreased in the single case that showed rapid evolution and short survival. Our data suggest that BAX/BCL-XL expression ratio may be a sensitive monitor of disease progression and an early predictor of TKI therapy responsiveness in CML patients.

Inverse shifting PCR based prenatal diagnosis of hemophilia-causative inversions involving int22h and int1h hotspots from chorionic villus samples

., 2008). The use of this method will facilitate anal-ysis of both inversions, although side-by-side analysisof Inv22 and Inv1 from the fetus sample is restricted toexceptional circumstances (outlined below).The aim of this report is to analyze the ability ofthe method of IS-PCR for PND on DNA extractedfrom chorionic villus (CV) samples. Because humangenome sequences are openly available in the web,specific IS-PCR approaches can be easily designed forgenotyping virtually any full-defined structural variants,thus providing a powerful tool to investigate otherdisease causative rearrangements from CV samples.In 2002, a pregnant carrier of HA, mother of a severeHA patient, whose Inv22 mutation had been identifiedin our laboratory, came to our attention for PND. Duringher twelfth week of gestation, a CV sample was obtainedand gender analyzed by karyotyping, indicating that thefetus was a female. The direct mutation identificationwas then attempted by Southern blotting (Lakich