Pamela Scarparo

Congenital factor X deficiencies with a defect only or predominantly in the extrinsic or in the intrinsic system : A critical evaluation

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 genotype‐phenotype 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., 2008.

Congenital prekallikrein deficiency

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.

Heparin-Induced Thrombocytopenia in Patients with Philadelphia-Negative Myeloproliferative Disorders and Unusual Splanchnic or Cerebral Vein Thrombosis

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.

Congenital FX deficiency combined with other clotting defects or with other abnormalities: a critical evaluation of the literature

Summary.  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.

Comparison of three different immunoassays in the diagnosis of heparin-induced thrombocytopenia.

Abstract Background: Heparin-induced thrombocytopenia (HIT) is caused by platelet activating antibodies that recognize platelet factor 4/heparin (PF4/H) complexes. Laboratory testing plays a key role in the diagnosis of HIT. As functional assays are unfeasible for most clinical laboratories, antigen binding assays are commonly used in routine testing. However, their low specificity leads to overdiagnosis of HIT. Therefore, it is advisable to improve screening tests in this setting. Methods: Blood samples from 114 patients in whom HIT was suspected were investigated using a chemiluminescence test (HemosIL® AcuStar HIT-IgG), a PF4/H IgG enzyme immunoassay (Lifecodes PF4 IgG), an IgG-specific lateral flow immunoassay heparin-induced thrombocytopenia (LFI-HIT, STic Expert® HIT) and the heparin-induced platelet aggregation (HIPA) test. Results: Twenty-nine (25.4%) out of 114 subjects with suspected HIT had a positive HIPA test. None of patients with a 4Ts score <4 were positive at HIPA. HemosIL® AcuStar HIT-IgG showed the best performance in term of sensitivity and specificity when used as single test. Receiver operating characteristic (ROC) analysis showed optimization of sensitivity and specificity using a cut-off of 1.13 U/mL (0.95 and 0.98, respectively). As an alternative approach, a strategy based on screening samples by STic Expert® HIT and then retesting positive results by Lifecodes PF4 IgG (cut-off 1 OD) or HemosIL® AcuStar HIT-IgG (cut-off 1.3 U/mL) showed a performance compared to a single test approach by HemosIL® AcuStar HIT-IgG. Conclusions: 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.

Persistent validity of a classification of congenital factor X defects based on clotting, chromogenic and immunological assays even in the molecular biology era.

Summary.  An adequate classification of congenital bleeding disorders is of great importance in clinical practice. This is true also for factor X (FX) deficiency. This defect is classified in two forms: type I (cases with low activity and antigen) and type II (cases with low activity and variable levels of antigen). The introduction of molecular biology techniques has allowed a classification based on the site of mutation (propeptide, Gla‐domain, catalytic domain etc.) or on the type of mutation (missense, nonsense, deletion etc.). However, with a partial exception for defects in the Gla‐domain, no site or type of mutation yields a constant and/or typical phenotype. Due to these difficulties, a classification based on clotting, chromogenic or immunological assays is still the most suited for clinical purposes. A satisfactory classification that takes into account recent advances of FX deficiency could read today as follows:

Genetic study in patients with factor XII deficiency : a report of three new mutations exon 13 (Q501STOP), exon 14 (P547L) and -13C>T promoter region in three compound heterozygotes

A group of 29 patients with congenital factor XII (FXII) deficiency belonging to nine distinct families have been investigated. All were cases of true deficiency in the sense that there was no discrepancy between FXII activity and FXII antigen. From a clotting point of view, 11 patients appeared homozygous, as both FXII activity and antigen were very low (≤1% and traces of antigen). In other words, they were cases with no cross-reactivity material. In the heterozygotes, FXII activity and antigen were about 50% of normal in all cases. The molecular studies revealed that seven patients were real homozygotes for the mutation −8G>C in the promoter region confirming the conclusions reported by coagulation tests. On the contrary, the remaining patients with a homozygote-like phenotype were instead found to be compound heterozygous for two distinct mutations. Three of these mutations were new mutations, namely the combination of −8G to C with 501Q to T (exon 13), 547P to L (exon 14) and −13C to T in the promoter, respectively. The remaining mutations seen were not new. It is interesting that all compound heterozygotes showed a clotting and immunological pattern similar to that shown by homozygotes, namely very low FXII activity and antigen. The new mutations were not present in the group of 98 normal persons of both sexes with the same geographical background. The wide diffusion of the −8G>C mutation in this group of patients coming from a limited geographical area suggests a founder effect. The significance and importance of genetic analysis in addition to clotting and immunological studies in FXII deficiency is emphasized.

Presence of anti-ADAMTS13 antibodies in obesity

Eur J Clin Invest 2012; 42 (11): 1197–1204

A large family from Argentina with prekallikrein deficiency due to a compound heterozygosis (T insertion in intron 7 and Asp558Glu in exon 15): prekallikrein Cordoba.

A family with prekallikrein deficiency (PK) from Argentina was investigated by molecular biology techniques. Parents were not consanguineous. Propositus had prolonged PTT but normal PT. Degree of prolongation of aPTT varied with the activator and showed shortening on prolonged incubation. Defect was fully corrected by normal, FXII, FXI, or high molecular weight kininogen (HMWK) deficient plasmas. Prekallikrein activity was 4% whereas prekallikrein antigen was normal and had a normal electrophoretic mobility. Propositus presented a thigh deep vein thrombosis. He was treated with LMWH and coumarin together with supportive stockings. An affected brother of the propositus had two myocardial infarctions and was on coumarin therapy. Other family members never showed thrombotic events. No bleeding tendency was ever noted. Children of probands showed PK activity of 50% of normal whereas antigen was normal.

Unexplained discrepancies in the activity--antigen ratio in congenital FX deficiencies with defects in the catalytic domain.

Studies on molecular biology have considerably enhanced our understanding of congenital coagulation disorders but have failed so far to supply tools for an adequate classification of defects. In fact, mutations in the same domain may give rise to different phenotypes. Conversely, mutations in different domains, controlled by different exons, may cause similar patterns. The 37 kindreds with congenital factor X (FX) deficiency, known to have a defect in the catalytic domain, have been evaluated in an attempt to investigate the genotype—phenotype relation. Discrepant results were obtained because about half kindreds showed a type I pattern, namely a concomitant decrease in FX activity and antigen. The other half showed a type II pattern, namely a decrease in FX activity with a normal or near normal FX antigen. In a few instances, the allocation of the kindred either to type I or to type II defect could not be reached, due to the lack of information about the antigen. The comparison of the kindreds in which the same mutation has been discovered by different investigations is not always possible also for lack of information. The study analyzes the need to have a multipronged approach to the study of congenital FX deficiency. The indication of a mutation in a given domain does not provide clear information about the phenotype.