Prenatal diagnosis of haemophilia B: the Italian experience.

This article describes prenatal diagnosis (PND) of haemophilia B (HB) within the framework of Italian haemophilia centres and genetics laboratories. The study details the experience from six haemophilia genetic centres (three in the North, one in the Centre and two in the South of Italy) and summarizes the different techniques used to perform PND of HB during the last 15 years. To date, the Italian HB database includes 373 characterized unrelated patients and their genetic information has permitted the identification of 274 carriers of childbearing age. This database represents the main instrument for timely and precise PND. Sixty-six prenatal diagnoses were performed on 52 HB carriers whose average age at the time was 34 (ranging from 24 to 44 years). In 44 cases, genetic counselling for carrier status determination was performed before pregnancy, while eight were not studied prior to pregnancy. Foetal samples were obtained by chorionic villus sampling in 52 cases, by amniocentesis in 12 while two were diagnosed by analysis of free foetal DNA obtained from maternal peripheral blood. In 35 (53%) pregnancies the foetus was female. For 31 men (47%), haemophilia status was determined by analysis of previously determined informative markers or familial mutations (12 affected and 19 unaffected). There may be more than one laboratory involved in the PND diagnostic pathway (providing DNA extraction, karyotype analysis, gender determination, maternal contamination detection, molecular diagnosis and sequencing). Good communication between all the parties, coordinated by the haemophilia centre, is essential for a successful and rapid process.

Factor VIII S373L: mutation at P1' site confers thrombin cleavage resistance, causing mild haemophilia A.

A novel CRM+ mutation, factor VIII position 373 serine to leucine substitution (FVIII 373-Leu) was identified during a survey of Factor VIII (FVIII) mutations. We have purified the variant protein from the patient's plasma in order to allow further characterisation of the molecule. The CRM+ plasma contained 120% Factor VIII antigen (FVIII:Ag) and 6% Factor VIII coagulant activity (FVIII:C). After purification the mutant FVIII was subjected to thrombin proteolysis, and was thereby activated 5.6-fold compared with 7-fold for wild type molecule. Subsequently, spontaneous inactivation of the mutant was much slower than noted for wild type FVIII. Western blot analysis using monoclonal antibodies demonstrated that thrombin cleavage of FVIII 373-Leu at positions 740 and 1689 were normal but that cleavage at position 372 was completely absent. Crystallographic coordinates of the active site of thrombin complexed to fibrinopeptide A were used to explore possible mechanistic reasons for the failure of thrombin to cleave the mutant FVIII at position 372. Steric hindrance between the mutant side chain and the side chain of the P1 residue was apparent. We conclude that the functional defect of FVIII 373-Leu results from the inability of thrombin to cleave the mutant at position 372-373, and propose that this is due to steric hindrance by the side chain of leucine 373, preventing correct formation of the enzyme substrate complex.

Identification of 217 unreported mutations in the F8 gene in a group of 1,410 unselected Italian patients with hemophilia A.

To provide a National database, 1,410 unrelated hemophilia A (HA) patients were investigated using screening methods denaturing high-performance liquid chromatography (DHPLC), conformational-sensitive gel electrophoresis (CSGE)] and/or direct sequencing. F8 gene mutations were identified in 877 (81%), 146 (82%), and 133 (89%) families with severe, moderate, or mild HA, respectively. Among the 382 different mutations detected, 217 (57%) have not previously been reported in the F8 Haemophilia A Mutation, Structure, Test and Resource Site (HAMSTeRS) database. Mutations leading to a null allele accounted for 82, 15%, and less than 1% of severe, moderate, or mild HA, respectively. A missense mutation was identified in 16%, 68%, and 81% of severe, moderate, or mild HA, respectively. They included 105 missense mutations (48%), 41 small deletions (19%), 25 splice site mutations (12%), 24 nonsense mutations (11%), 18 insertions (8%), three large deletions (1%), and one deletion plus insertion. Unreported mutations were distributed throughout the F8 gene, as they affected all F8 exons but exon 20. We report a wide spectrum of mutations collected in a large National database. The type of mutation was a strong predictor of the clinical phenotype. This database is expected to considerably improve the genetic counseling and medical care of HA families in Italy.

Insight into molecular changes of the FIX protein in a series of Italian patients with haemophilia B.

Deficiency or dysfunction of factor IX FIX leads to haemophilia B (HB), an X-linked, recessive, bleeding disorder. On a molecular basis, HB is due to a heterogeneous spectrum of mutations spread throughout the F9 gene. In several instances, a cause-effect relation has been elucidated, in others predicted possibilities have been offered by crystallography inspection and by software-constructed models of the protein. The aim of this study was to contribute to the understanding of HB molecular pathology. The F9 missense mutations we identified in 21 unrelated Italian HB patients by direct sequencing of the whole F9 coding regions were inspected for the causative effect they provoked on the ensuing transcript, and on the protein structure. Each alteration was studied in order to: (i) characterize the defect on the basis of the nature of the mutation; (ii) identify the predicted defect that is induced in the gene and (iii) speculate about the potential, detrimental effects which upset the protein functionality through an idealized FIX model. The resulting data may further contribute to the comprehension of the mechanisms underlying the disease.

Carrier detection and prenatal diagnosis of hemophilia B with more advanced techniques.

We used the PCR to amplify three polymorphic regions of Factor IX gene on 35 Italian families: DdeI intron 1, Mn1I exon f, and the polymorphism HhaI located 8 kb at the 3' end of FIX gene. We analyzed the Mn1I and HhaI markers on DGGE and DdeI polymorphism on agarose gel. We reached an informativity of 78% and we found one mutation at codon 145 (exon f) during the screening for Mn1I polymorphism. Furthermore, we performed 16 prenatal diagnoses on chorionic villus samples; five were female and 11 male. Four were uninformative three healthy and one affected male fetus were recognized by PCR techniques, two healthy and one affected fetus by Southern analysis. In three pregnant women examined for the first time during pregnancy, the PCR technique allowed us to perform a rapid diagnosis of noncarrier status, avoiding the fetal sampling procedures.

Concomitant Turner syndrome and hemophilia A in a female with an idic(X)(p11) heterozygous at locus DXS52.

A 46,X,idic(X)(p11) karyotype was found in a female affected by Turner syndrome and sporadic moderate hemophilia A. Restriction fragment length polymorphism analysis of the patients's DNA demonstrated that the idic(X) contained alleles from both maternal X chromosomes. Since the idic(X) appeared to be always inactivated, a de novo mutation of factor VIII in the normal paternal X chromosome is probably responsible for the patient's coagulation disorder.

Recurrent antiphospholipid-related deep vein thrombosis as presenting manifestation of systemic lupus erythematosus.

UNLABELLED: Antiphospholipid antibodies (aPL) are frequently associated with thrombotic disorders in the so-called antiphospholipid syndrome. Together with anticardiolipin antibodies (aCL), lupus anticoagulant (LA) is the main diagnostic tool for aPL detection. Since LA determination is based on the finding of prolonged clotting time in vitro, concomitant anticoagulant therapy may significantly interfere with its detection. We report a case of a boy in whom recurrent aPL-related thrombosis heralded for several months the onset of systemic lupus erythematosus (SLE). Abnormally increased in vitro clotting times at the time of the second thrombotic event led to the suspicion of the presence of LA activity. However, this latter finding was difficult to interpret since the patient was already on heparin treatment at the time of our first observation. Thus, LA was assayed using a commercial kit in which a heparin neutralizer is included (Staclot LA). Two consecutive samples from the patient were compared with eight patients on anticoagulant therapy for non-aPL-related thrombotic events and 20 healthy controls. The study showed that, taking into account the concomitant anticoagulant treatment, Staclot LA was positive only in the propositus, raising the suspicion of a possible aPL-related origin of the thrombotic event. This issue was definitively confirmed in a subsequent follow-up. CONCLUSION: The present report shows that aPL-related deep vein thrombosis can be the earliest clinical manifestation of pediatric SLE, and that Staclot LA may have a role in LA detection during the course of anticoagulant treatment.

A new strategy for prenatal diagnosis in a sporadic haemophilia B family.

Although the quality of life for haemophiliacs has clearly improved in the last few years, haemophilia still remains a serious disorder justifying prenatal diagnosis (PD) and, if necessary, termination. Because chorionic villus sampling (CVS) is performed in the first trimester of pregnancy, an increasing number of carriers are interested in this test. It has been shown that waiting for the results is particularly distressing for pregnant women, therefore decreasing the diagnostic procedure time can be psychologically helpful. Here we report on PD in a sporadic haemophilia B family based on the direct identification of the pathogenic mutation in a CVS taken at the 12th gestational week. In order to hasten the results, we recovered DNA from a single villus fragment boiled in water and used it directly for PCR reaction. Conformation-sensitive gel electrophoresis (CSGE) was used to detect the mutation in the haemophilia carrier and in the foetus. This approach allowed us to obtain a diagnosis within 24 h of CVS, thus avoiding the long-term psychological effects on the pregnant woman.

Germ-line origin of intron 1 inversion in two haemophilia A families.

Factor VIII gene inversion of intron 1 has recently been reported to be the mutation responsible for haemophilia A in about 5% of severe cases. In our series of patients, which is made up of 77 Italian cases negative for intron 22 inversion, the mutation was found in three sporadic and in one familial patients, with an overall frequency of 5.2%. The carrier status of the patients' female relatives was assessed by mutation analysis and showed that only two-thirds of cases could be considered truly sporadic. The germ-line origin of the mutation was investigated in the two sporadic families by haplotype analysis on genomic DNA of the patients' maternal grandparents. These studies indicated that both mutation events had occurred in the germ cell lines of the patients' healthy grandfather, suggesting that, as already demonstrated for the inversion of intron 22, the male germ cell line is more susceptible to the intrachromosome recombination which leads to the inversion of intron 1.