The congenital deficiency of prekallikrein (PK) is a rare condition in which there is a peculiar discrepancy between a severe in vitro defect and absence of bleeding. The gene controlling PK synthesis is located on chromosome 4 and consists of 14 exons and 15 introns. Only approximately 80 cases of PK deficiency have been described in the literature. Owing to the lack of bleeding, most cases go undetected or, if detected, go unreported. Occasional bleeding or thrombosis have been reported in a few patients but this was only due to the presence of associated risk factors. It is certain that the defect does not protect from thrombosis. Diagnosis is based on the presence of a great prolongation of partial thromboplastin time and normal prothrombin time and thrombin time. The long partial thromboplastin time is fully corrected by the addition of normal plasma or normal serum and presents the unusual feature of shortening on long incubation times. Platelet and vascular tests are normal. Immunological studies allow differentiation into two types, namely cases of true deficiency, which are approximately 70% of the total, and cases with abnormal forms. PK is a glycoprotein synthesized in the liver as a single-chain peptide of 88000 Da. It mostly circulates (∼75%) as a complex with high-molecular-weight kininogen. It is cleaved by FXIIa into a heavy chain and a light chain (catalytic domain), held together by disulfide bonds. Molecular biology techniques have so far only been applied to eleven families, and these studies do not yet allow definite phenotype/genotype conclusions. The exons involved are 5, 8, 11, 14 and 15. The noncoagulative effects of PK, mainly based on the effect of kallikrein, have been studied less, since they appear to be the result of the involvement of other components of the contact phase. Kallikrein can mainly affect the formation of bradykinin from high-molecular-weight kininogen and the activation of pro-urokinase to urokinase. Bradykinin causes inflammation, vasodilatation and an increase in vessel permeability. The activation of pro-urokinase results in enhanced fibrinolysis. However, fibrinolysis has been reported to be normal or defective in these patients.

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Congenital Factor X deficiency is commonly classified as type I, in which there is a concomitant decrease of activity and antigen (CRM negative), and in type II, in which activity is low but antigen is normal or near normal (CRM positive). During the past decades it was shown that type II was by itself very heterogeneous. It was shown in fact that some forms showed a defect in all three assay systems (extrinsic, intrinsic, and RVV dependent), whereas others showed a defect only in two of the three systems. Molecular biology analysis, whenever available, has failed so far to supply clear explanations for these discrepancies. The purpose of the present article was an attempt to correlate the clotting activities seen in these two defects with other clotting, chromogenic, immunological assays, and molecular biology results. There are in the literature 10 families that show a predominant defect in the extrinsic system, and four families that show a predominant defect in the intrinsic system. All patients showed a normal, near normal, or reduced level of antigen that is always definitively higher than the clotting counterpart. Molecular biology studies revealed mutations in different exons, namely 2, 4, 5, 6, and 8. These mutations in different exons do not allow any clear genotypephenotype conclusions, but indicate that mutations in different exons may give rise to the same phenotype. The study underlines the importance of a multipronged evaluation of all cases with Factor X deficiency. In fact only by this approach can an acceptable classification of the defect be reached. Am. J. Hematol. 83:668-671, 2008. V

The HemosIL® AcuStar HIT or a combinatorial approach with the STic Expert® HIT and the PF4/H IgG enzyme immunoassay provide an accurate diagnosis of immune HIT.

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The presence of more than one congenital clotting defect in a given patient is a rare event but not an exceptional one. Combined defects of factor X (FX) are very rare because congenital isolated FX deficiency is by itself very rare. A perusal of personal files and of the literature has yielded 12 families with FX deficiency in which an association with another clotting factor deficiency was found. The associated defects were factor VII (FVII) or factor VIII (FVIII) or factor XII (FXII) deficiency. By far the most frequently associated was with FVII. Two forms of this association were found. In the first form there is casual association of both FVII and FX deficiency in the proband with independent recessive segregation of the two defects in other family members. The second form is because of abnormalities in chromosome 13 (deletions, translocations and so on) involving both FX and FVII genes. These genes are known to be very close and located on the long arm of chromosome 13 at about 13q34. In this form the hereditary pattern is autosomal dominant. Isolated FX deficiency and, more frequently, combined FX + FVII deficiency appear also associated with coagulation-unrelated abnormalities (carotid body tumours, mitral valve prolapse, atrial septal defect, ventricular septal defect, thrombocytopenia absent radius (TAR) syndrome, mental retardation, microcephaly and cleft palate). Diagnosis of a combined clotting defect could be difficult on the basis of global tests. For example, both isolated FX deficiency and combined FX + FVII deficiency yield a prolongation of basal PTT and PT. Only specific assays could allow one to reach the correct diagnosis. In cases of casual association with other defects, it is also important to study family members, as the two defects should segregate independently.

Background: Philadelphia-negative myeloproliferative disorders (Ph-MPD) are common causes of unusual splanchnic or cerebral vein thrombosis, which is treated with unfractionated heparin (UFH) or low-molecular-weight heparin (LMWH). Heparin-induced thrombocytopenia (HIT) is a dangerous potential complication of this therapy, but it has rarely been reported in Ph-MPD. Patients and Methods: We retrospectively reviewed clinical records of 29 patients with Ph-MPD who have been treated with UFH or LMWH for unusual splanchnic or cerebral vein thrombosis (3 cerebral sinus, 6 portal and 20 hepatic vein). The goal of the study was to determine the occurrence of new thrombotic events during heparin therapy secondary to HIT (HITT). Results: During heparin therapy, 5 out of the 29 patients (17%) developed a new thrombotic episode (pulmonary embolism) with a high clinical probability of HIT based on the 4 T’s score even though not all the patients developed ‘true’ thrombocytopenia. A diagnosis of HIT was established in 2 patients (6.8%) through the presence of heparin-related antibodies. Conclusions: Ph-MPD patients on heparin warrant careful monitoring and HIT has to be suspected whenever platelet counts drop or a new thrombosis is detectable.