Von Willebrand disease in children: diagnosis and management of a pediatric cohort in one single center in Argentina.

Clinical and laboratory data of children with von Willebrand disease (VWD) types have been derived from retrospective studies and small case series. This article reports on the clinical and laboratory data of a large pediatric cohort in one single Argentinian center. The biological and clinical responses to desmopressin and replacement therapies are also described. Over a 15-year period, 194 of 1150 children (16.9%) were diagnosed as having type 1 VWD (80%), type 2 VWD (19%), and type 3 VWD (1%). The distribution of the different type 2 VWD subtypes was type 2A VWD, 43%; type 2B VWD, 32%; type 2M VWD, 19%; and type 2N VWD, 6%. Eighty patients with type 1 VWD and 12 patients with type 2 VWD were prospectively evaluated to desmopressin (DDAVP) response. A complete response was observed in all children with type 1 VWD, whereas 40% of the children with severe type 1 VWD and with type 2 VWD achieved a complete response. All the children who received DDAVP as prophylaxis or treatment for bleeding had good clinical evolution. Considering the restricted availability of specialized hemostasis centers, we believe our clinical and laboratory approach appropriate for the detection of patients with different types of VWD. Further studies are necessary to determine epidemiological aspects of VWD in Argentina to estimate the necessary facilities and trained personnel for the diagnosis and management of patients with VWD.

Association between insulin resistance and risk of complications in children and adolescents with type 1 diabetes.

BACKGROUND: It has been hypothesized that insulin resistance may be involved in the development of type 1 diabetes complications and early diagnosis would be important for their prevention. Our aim was to study insulin resistance in our population of children with type 1 diabetes and to identify associated early risk factors for micro- and macrovascular complications. METHODS: A descriptive, cross-sectional study was conducted including 150 children with type 1 diabetes. Anthropometric, bioelectric impedance, carotid Doppler ultrasonography, electromyography, and conduction velocity studies were performed. Baseline plasma glucose, lipid profile, uric acid, plasma thyrotropin, glycosylated hemoglobin A1C, and microalbuminuria were assessed. More insulin-resistant patients were defined as those having an estimated glucose disposal rate (eGDR) value below the first quartile. RESULTS: Clinically manifest microvascular complications were not found in any of the patients. More insulin-resistant patients had a greater sub scapular fold thickness, a higher incidence of obesity (12% vs. 1.7% p 0.007), higher fructosamine levels (496 vs. 403 p<0.00019, and a higher incidence of altered lipid metabolism (70% vs. 39% p 0.0007). CONCLUSION: In the subgroup of patients with lower eGDR there were more children with lipid disorders, obesity, and worse diabetic control, which, if not corrected, may lead to development of micro- and macrovascular complications.

Factor V Leiden and prothrombin gene G20210A mutation in children with venous thromboembolism.

To determine whether factor V Leiden (FVL) and/or prothrombin gene G20210A mutation (PT20210A) are risk factors for venous thromboembolism (VTE) in Argentinean children. One hundred and thirty consecutive children with VTE were prospectively assisted at a single centre. Blood samples were available from 110 of them for detailed haematological analysis. The prevalence of both mutations was compared with a control group. The odds ratio for VTE was significantly increased in patients with FVL (OR 3.64; 95% CI: 1.14-11.6, p < 0.029) whereas odds ratio for VTE was not significantly increased in patients with PT20210A (OR 1.06; 95% CI: 0.24-4.73, p = 0.938). Combined disorders were found in 5 of the 10 children with the aforementioned mutations. In 21 children (19%) without these mutations other inherited and acquired disorders were detected. Our data show that FVL is a risk factor for VTE whereas PT20210A does not seem to be a risk factor in our paediatric population.

Antithrombin.

Antithrombin (AT) is a heparin cofactor and a member of the serine protease inhibitor family (serpin). The mature AT molecule is composed of 432 amino acids and it is produced mainly in the liver. Initially, several different AT activities in plasma were reported, leading to the classification of antithrombin in a range from I to IV. It was subsequently shown that these various antithrombin activities were the function of one molecule, antithrombin III, whose name was reduced to antithrombin at the meeting of the International Society in Thrombosis and Haemostasis in 1993. AT is an important protease inhibitor of thrombin and factor Xa. However, AT is also able to inhibit factors IXa, XIa, XIIab, kallikrein, and plasmin. Given that AT is one of the major naturally occurring inhibitors of coagulation, acquired or hereditary deficiencies of this protein result in excessive thrombin generation. As a vast array of mutations are responsible for hereditary AT deficiencies, screening for their presence by DNA testing would require sequencing each entire gene involving numerous exons. Moreover, the knowledge of the gene mutation does not offer any benefit in the treatment of affected families, so the routine molecular characterization is not indicative. These defects are detected by functional or immunological assays. AT amidolytic assays are recommended for initial testing for AT deficiency. There is no need to routinely perform AT immunological assays. However, they are useful in order to distinguish type I from type II hereditary AT deficiency.

Protein C.

Protein C (PC) is a 62-kDa vitamin K-dependent plasma zymogen which, after activation to serine protease, plays an important role in the physiologic regulation of blood coagulation. Given that PC is one of the major naturally occurring inhibitors of coagulation, acquired or hereditary deficiencies of this protein result in excessive thrombin generation. As a vast array of mutations are responsible for hereditary PC deficiencies, screening for their presence by DNA testing would require sequencing each entire gene involving numerous exons. Moreover, the knowledge of the gene mutation does not offer any benefit in the treatment of thrombophilic families, so the routine molecular characterization is not indicative. These defects are detected by functional or immunological assays. Measurement of PC activity is essential to identify subjects with both type I and type II PC defects. There is no need to routinely perform PC immunological assays. However, they are useful in order to distinguish type I from type II PC hereditary deficiency.

Protein S.

Protein S (PS) is a vitamin K-dependent plasma glycoprotein. Around 60-70% of PS in plasma is noncovalently bound to C4-binding protein (C4BP). Free PS functions as a cofactor that enhances the activity of activated protein C (APC) in the proteolytic degradation of activated factors V and VIII. PS also has a more recently described APC-independent ability to directly inhibit prothrombinase and tenase by direct binding of activated factors V, VIII, and X. Given that PS is one of the major naturally occurring inhibitors of coagulation, acquired or hereditary deficiencies of this protein result in excessive thrombin generation. As a vast array of mutations are responsible for hereditary PS deficiencies, screening for their presence by DNA testing would require sequencing each entire gene involving numerous exons. Moreover, the knowledge of the gene mutation does not offer any benefit in the treatment of thrombophilic families, so the routine molecular characterization is not indicative. These defects are detected by functional or immunological assays for free and total PS forms. Given that functional PS assays may detect some forms of PS deficiency that free PS immunoassays may miss, it is recommended to include them for initial testing along with immunoassays for free PS, although they should be used with caution. Functional PS assays are subject to multiple interference. For example in the presence of lupus anticoagulant (LA), only free PS immunoassays are recommended for initial testing. PS antigen assays are more popular with most laboratories.

Prospective study of low-dose ristocetin-induced platelet aggregation to identify type 2B von Willebrand disease (VWD) and platelet-type VWD in children.

Type 2B von Willebrand disease (VWD2B) and platelet-type von Willebrand disease (PT-VWD) are rare bleeding disorders characterised by an increased ristocetin-induced platelet aggregation (RIPA) at low dose of ristocetin. It was the objective of this study to detect children with VWD2B and PT-VWD using RIPA at low dose of ristocetin (0.5 mg/ml) in the screening evaluation of bleeding disorders, and to analyse the phenotypic data along with the molecular findings. Over a 14-year period, 641 children with personal and family bleeding symptoms or bleeding from birth with previously uncharacterised haemostatic disorders were prospectively studied. Six unrelated patients (0.93%) showed RIPA at low dose of ristocetin. RIPA-based mixing studies identified that the plasma of the six probands and at least one parent from five unrelated families induced aggregation of normal platelets with the addition of low-dose ristocetin. None of the probands' platelets showed aggregation with cryoprecipitate. Low ristocetin cofactor activity/VWF antigen ratio with absent collagen binding activity or thrombocytopenia were detected respectively in only two patients. Molecular analysis of exon 28 of the VWF gene identified mutations in only three patients. No mutation in the GP1BA gene was found. In this large prospective paediatric study, the screening approach including RIPA at low dose of ristocetin permitted the detection of patients with VWD2B that would otherwise have been missed. No patient with phenotype or genotype of PT-VWD was identified. Heterogeneity of bleeding symptoms and phenotypic parameters were found among members of the same family.

Arterial ischemic stroke and cerebral venous thrombosis in children: a 12-year Argentinean registry.

Over a 12-year period, 112 consecutive children with arterial ischemic stroke (AIS) and 38 children with cerebral venous thrombosis (CVT) were prospectively recruited at a single pediatric center in Argentina. One or more underlying clinical conditions were identified in most patients (55%) with AIS and in almost all patients with CVT. Inherited and/or acquired prothrombotic disorders were detected in 17% of the patients with AIS and in 34% of the children with CVT. No associations between factor V Leiden or prothrombin G20210A mutation and children with AIS or CVT were found. Antithrombotic agents (i.e., aspirin, low-molecular-weight heparin and acenocoumarol) were administered without major hemorrhagic complications. In our cohorts, mortality due to the thrombotic episode was 1.8% in children with AIS. No child with CVT died from his or her thrombotic episodes. Three children (3.2%) and 1 adolescent (1.1%) with AIS had thrombotic progression and recurrence, respectively. A large percentage of children with AIS (68%) and CVT (32%) have had some kind of sequels that caused serious disability in approximately half the cases.

Factor V Leiden and prothrombin gene G20210A mutation in children with cerebral thromboembolism.

We investigated whether there is an association between factor V Leiden (FVL) and/or prothrombin gene G20210A mutation (PT20210A) and cerebral thromboembolism in a pediatric Argentinean population. From May 1992 to January 2002, 44 consecutive children with arterial ischemic stroke (AIS) and 23 children with cerebral sinovenous thrombosis (SVT) were prospectively studied at a single center. The prevalence of both mutations was compared with a 102 age-matched controls. In children with AIS, the frequencies (patients vs. controls), odds ratio (OR), and 95% confidence interval (95% CI) for the presence of FVL were as follows: 2.3% vs. 2%, OR/95% CI, 1.16/0.2 to 13.2; P value = 0.99. No cases of PT20210A were found in this group. In children with SVT, the frequencies (patients vs. controls), OR, and 95% CI were as follows: FVL (4.3% vs. 2%, OR/95% CI, 2.27/0.22 to 6.2; P value = 0.99) and PT20210A (4.3% vs. 1%; OR/95% CI, 4.6/0.3 to 76.3; P value = 0.3354). One child with PT20210A also had an inherited protein C deficiency. In 12 (18%) out of the 67 children with cerebral thromboembolism, without the aforementioned mutations, other prothrombotic disorders were detected. Although a multi-center prospective study with a large number of Argentinean pediatric patients is needed to obtain considerable evidence, no association between factor V Leiden and/or prothrombin gene G20210A mutation and cerebral thromboembolism was found in this pediatric series.