Twenty-two molecular diagnostic laboratories from 14 countries participated in a consortium study to estimate the impact of Factor VIII gene inversions in severe hemophilia A. A total of 2,093 patients with severe hemophilia A were studied; of those, 740 (35%) had a type 1 (distal) factor VIII inversion, and 140 (7%) showed a type 2 (proximal) inversion. In 25 cases, the molecular analysis showed additional abnormal or polymorphic patterns. Ninety-eight percent of 532 mothers of patients with inversions were carriers of the abnormal factor VIII gene; when only mothers of nonfamilial cases were studied, 9 de novo inversions in maternal germ cells were observed among 225 cases (approximately 1 de novo maternal origin of the inversion in 25 mothers of sporadic cases). When the maternal grandparental origin was examined, the inversions occurred de novo in male germ cells in 69 cases and female germ cells in 1 case. The presence of factor VIII inversions is not a major predisposing factor for the development of factor VIII inhibitors; however, slightly more patients with severe hemophilia A and factor VIII inversions develop inhibitors (130 of 642 [20%]) than patients with severe hemophilia A without inversions (131 of 821 [16%]).

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Antiphospholipid antibodies (APA) are often associated with severe clinical manifestations, especially in the setting of systemic lupus erythematosus (SLE). Here we have investigated the prevalence of anticardiolipin antibodies (aCL) and lupus anticoagulant (LA) in paediatric patients affected with SLE, JCA and overlap syndromes (OS) and correlated the presence of aCL and LA with clinical features. aCL were assayed by enzyme-limited immunoassay; LA was determined by activated partial thromboplastin time and the kaolin clotting time test. aCL and LA assays were performed in parallel on at least two occasions over a 7-30-month follow-up. Fifteen out of nineteen (79%) SLE patients had aCL and 8/19 (42%) had LA. Six SLE patients displayed manifestations that were APA-related: deep venous thromboses, autoimmune haemolytic anaemia, pulmonary hypertension, neurological alterations. Five out of six symptomatic patients had both LA and high-titre aCL. In contrast, JCA and OS patients had usually low-titre aCL, no detectable LA and no APA-related manifestations. aCL persisted at high titre over time in SLE patients, but was only transiently detected in JCA and OS patients. This study shows that the simultaneous positivity for LA and high-titre aCL allows the identification of paediatric SLE patients who are at risk not only for thrombosis, but also for other APA-related clinical features.

SummaryA 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 (FVIILAg) and 6% Factor Vili coagulant activity (FVIILC). 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 PI 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.