Activated protein C resistance in a neonate with venous thrombosis

Thromboembolic disease and antithrombotic therapy in newborns

This update uses an evidence based approach to analyze and present the epidemiology of neonatal thrombosis, etiologies, currently used techniques for diagnosis with their limitations, and current therapeutic approaches. In addition, the approaches to both prevention and optimal therapies are discussed. In Section I Dr. Paul Monagle addresses the epidemiology of neonatal thrombosis outside of the central nervous system in both arterial and venous locations, and those that occur in utero. The specific contributions of catheters and congenital prothrombotic disorders are delineated. Dr. Monagle also describes currently used techniques for the diagnosis of thrombotic events as well as their limitations and the current therapeutic approaches. In Section II, Dr. Gabrielle deVeber reviews the epidemiology of neonatal thrombosis within the central nervous system, in both arterial and venous locations and those that occur in utero. The neurological presentation, risk factors including congenital prothrombotic disorders, anatomical distribution, diagnostic tests, use of antithrombotic therapy and neurologic outcome of neonates with either sinovenous thrombosis or arterial ischemic stroke are discussed. In Section III, Dr. Anthony Chan reviews the current approaches to the prevention and treatment of neonatal thrombosis. Information on the differences in the response of neonates compared to adults to antithrombotic therapy and new approaches to the prevention and treatment of thrombosis in neonates are emphasized.

Inherited thrombophilia: a possible cause of in utero vascular thrombosis in children with intestinal atresia

BACKGROUND

Congenital atresia of the small and large intestine is thought to evolve from in utero mesenteric vascular occlusion of the corresponding intestinal segment. Because spontaneous thrombosis recently has been described in association with inherited thrombophilia, the authors wondered if inherited thrombophilia also might be found in babies with intestinal atresia.

METHODS

Genetic analysis was done on 28 children treated for congenital intestinal atresia. DNA was analyzed for point mutations to detect the 2 most common types of inherited thrombophilia, the G1691A mutation in the factor V gene (factor V Leiden) and the G20210A mutation in the prothrombin gene. In addition, other genetic risk factors for thrombosis were analyzed including the C677T mutation in the methylenetetrahydrofolate reductase gene (MTHFR) and 2 polymorphisms of the factor VII gene (the R353Q and the hypervariable region 4 polymorphisms).

RESULTS

The factor V Leiden mutation was present in 5 of 28 (18%) children treated for congenital intestinal atresia. This is increased significantly when compared with the reported carrier frequency of 3% to 7% in the general population and a reported carrier rate of 4.2% in the local population (P <.005). The R353Q polymorphism of the factor VII gene, specifically the RR genotype, was noted in 85% of patients with atresia with an expected frequency of 64% (P <.008). There were no significant associations noted between mutations in the prothrombin gene, the MTHFR gene, or the hypervariable region of the factor VII gene.

CONCLUSIONS

The factor V Leiden mutation and the RR subtype of the R353Q polymorphism of the factor VII gene are seen at an increased frequency in children with congenital intestinal atresia. This suggests that inherited thrombophilia may play a role in the etiology of these in utero mesenteric thrombotic events.

Left brachial artery thrombus, left axillary vein thrombus, and stroke in a neonate with factor V Leiden mutation

Factor V Leiden mutation is reportedly the most common hereditary risk factor for thrombosis. Spontaneous venous thromboses in children with factor V Leiden are rare without the presence of an additional risk factor for thrombosis. Spontaneous arterial thromboses are even more rare. In this case report, we describe an unusual case of a neonate born with both arterial and venous thromboses involving the left brachial artery, the left brachial vein, and stroke involving the right middle cerebral artery. The infant was subsequently found to be heterozygous for the factor V Leiden mutation. His mother was also heterozygous for the mutation but did not have a history of thrombosis. Evaluation for the factor V Leiden mutation should form part of the work-up of an infant with either arterial or venous thromboses or stroke because it increases the infant's relative risk for future thrombosis.

Upregulation of the antithrombotic protein C pathway at birth

Serious thrombotic complications occur in sick neonates, while healthy infants have a very low risk of thrombosis. To better understand the regulation of physiological anticoagulation at birth, components of the protein C pathway were measured in cord plasma samples from 14 full-term healthy newborns and in samples from 10 adult controls. Although zymogen protein C was significantly reduced in cord plasma (mean +/- SEM in cord vs. adult sample 37 +/- 1.4% vs. 90 +/- 5.5%, p < 0.0001), levels of the active enzyme, activated protein C (APC), were not (119 +/- 20% vs. 75 +/- 12%, p = 0.0762). Relative to the protein C level, cord plasmas had a 5.2-fold higher APC level (p < 0.01). The APC increase was partially due to slower inactivation of APC in cord plasma (half-life for APC 50 min in cord plasma vs. 27 minutes in adult plasma). Increased sensitivity of factor V to inactivation by APC in cord plasma was observed since the activated partial thromboplastin time-based APC sensitivity ratio was significantly increased for cord vs. adult plasma samples (2.28 +/- 0.09 versus 1.97 +/- 0.03, p < 0.01). Thus, despite low zymogen protein C, the protein C pathway in newborns seems to be functionally well developed and at an activated stage at birth.

Legg-Perthes disease in three siblings, two heterozygous and one homozygous for the factor V Leiden mutation

A family is described with three-generation transmission of factor V Leiden (a thrombophilic mutation that causes resistance to activated protein C). Legg-Perthes disease developed in three siblings in this family. The male proband and his sister were heterozygous for the mutation and had unilateral hip disease at age 2 years. The brother, who had bilateral hip disease, was homozygous. This novel family provides compelling evidence for the pathoetiologic role of familial thrombophilia in Legg-Perthes disease.

Stroke in a neonate heterozygous for factor V Leiden

Activated protein C resistance is the most common hereditary coagulation abnormality and is caused by the factor V Leiden mutation. A newborn who developed seizures within hours after delivery and was found to have a bihemispheric stroke is described. This patient, determined to be heterozygous for factor V Leiden, is the first reported case of neonatal stroke associated with this common mutation.

Bilateral renal vein thrombosis and venous sinus thrombosis in a neonate with factor V mutation (FV Leiden)

Bilateral renal vein thrombosis and venous sinus thrombosis were diagnosed within 3 weeks of birth in a full-term neonate. Heterozygosity for a factor V mutation leading to resistance against the anticoagulatory properties of activated protein C was found. Heparin therapy led to resolution of the thrombotic manifestations. With long-term oral anticoagulation, no relapse or other thrombotic event occurred during infancy.

Prevalence of factor V Leiden in children with thrombo-embolism

Hereditary resistance to the anticoagulatory action of activated protein C (APC resistance, APCR) was identified as a possible new thrombophilic factor in a high percentage (17%-60%) of young adults with thrombotic events. A single missense mutation (R506Q) due to a G/A transition (G1691A) in exon 10 of the factor V gene is regarded as the causative molecular defect, resulting in factor V Leiden which is correlated with APCR. Identification of this mutation by polymerase chain reaction-based methods is easy to perform and prevents pre-analytical and analytical errors in the coagulometric assay for APCR. Since the impact of this mutation in children with thrombo-embolic disease has not been determined to date, we initiated a multi centre prevalence study in two paediatric populations, with and without thrombo-embolic events. We compared 125 paediatric patients with thrombosis, divided into three different age groups (0 to < 0.5 years; > 0.5 to < 10 years; > 10 to < 18 years) with a normal population of 159 children. Although the mutation G1691A was found with an unexpectedly high prevalence of 12% in our normal controls, the prevalence was significantly higher in the age groups; 0 to < 0.5 years (26%) and > 10 to < 18 years (30%). In patients between > 0.5 and < 10 years the overall prevalence was similar to that of the control group (13%). However, in patients of this age with spontaneous thrombosis, G1691A was also a significant risk factor (5/17 approximately equal to 29%). Homozygosity for G1691A was detected in three patients but not in the control group. Including deficiencies of protein C, protein S, antithrombin, and the presence of anti-phospholipid antibodies, thrombosis was correlated with endogenous thrombophilic factors in 38/125 patients (30.4%).

CONCLUSION

Our results emphasize the impact of factor V Leiden on thrombogenesis in children. However, the significance is age-dependent and may reflect the different physiology of haemostasis in the three age groups. The diagnostic workup of children with thrombosis should include tests for factor V Leiden. The correlation of factor V Leiden with the clinical course of thrombo-embolism in children is essential to establish rational guidelines for therapy and prophylaxis of APCR-related thrombosis which are not yet available.

Inherited defects of the protein C anticoagulant system in childhood thrombo-embolism

Childhood thrombo-embolism is mostly the result of inherited thrombophilia or vascular insults combined with risk factors such as peripartal asphyxia, fetopathia diabetica, exsiccosis, septicaemia, central lines, congenital heart disease, cancer, trauma, surgery or elevated antiphospholipid antibodies. Inherited thrombophilia includes mainly defects of the protein C pathway, resistance to activated protein C, protein C or protein S deficiency. Resistance to activated protein C, in the majority of cases caused by the point mutation Arg 506 Gln of the factor V gene, has emerged as the most important hereditary cause of thrombo-embolism in adults and children. However, since an acquired risk of thrombo-embolic complications frequently masks the inherited deficiency in affected children, children with thrombo-embolism should have adequate laboratory evaluation for inherited coagulation disorders, especially the protein C pathway. Until more data on childhood thrombo-embolism are available, treatment recommendations will continue to be extrapolated from guidelines for adults.

Factor V Q 506 mutation in children with thrombosis

The factor V Leiden mutation in 12-children with thrombosis and in 20 controls was investigated. Five heterozygous individuals and 1 homozygous individual among the cases with thrombosis and 1 heterozygous individual among controls were found. Central nervous system thromboses were increased in children with the factor V mutation, associated with protein S deficiency.

Neonatal purpura fulminans in association with factor V R506Q mutation

We report a case of neonatal purpura fulminans associated with activated protein C resistance. Analysis of DNA demonstrated heterozygosity for the factor V R506Q mutation. The neonate, at 8 hours of age, had progressive purpuric skin lesions and later had evidence of microvascular, hemorrhagic thrombosis in the brain. The baby was treated with fresh frozen plasma infusions and had complete resolution of the skin lesions and no apparent long-term complications. We suggest that activated protein C resistance testing be included in the initial evaluation of neonatal purpura fulminans.

ARMS test for diagnosis of factor VLeiden mutation, a common cause of inherited thrombotic tendency

We developed a simple and rapid amplification-refractory mutation system (ARMS) assay for the factor V mutation [R506Q] (factor VLeiden), which results in the autosomal dominant thrombotic tendency, resistance to activated protein C (rAPC). PCR primers within Exon 10 of the factor V gene were designed. A common upstream primer was paired with either a mutant or wild-type-specific downstream primer. The 3'-most nucleotide of the specific primers recognized either the mutant or normal allele, and the 3' penultimate nucleotide was mismatched to enhance specificity of the reaction. The assay was validated using authentic factor VLeiden DNA samples. Seven of 103 hematologically normal children (6.8%) were found to be heterozygotes. Among 27 patients studied by the rAPC assay, ARMS assay and rAPC results were concordant in 26. Among these were a 1-year-old child with a calcified clot in the inferior vena cava. Both the patient and his father were heterozygous for the mutation and both had abnormal rAPC assays. rAPC and factor VLeiden assays were discordant in a young girl with a history of stroke. Biochemical rAPC assay was abnormal, while ARMS assay revealed amplification only with wild-type primers, suggesting a non-[R506Q] mechanism for rAPC. This assay will be a valuable tool for studying subjects with thromboses and their family members.

ARMS test for diagnosis of factor VLeiden mutation, a common cause of inherited thrombotic tendency

We developed a simple and rapid amplification-refractory mutation system (ARMS) assay for the factor V mutation [R506Q] (factor VLeiden), which results in the autosomal dominant thrombotic tendency, resistance to activated protein C (rAPC). PCR primers within Exon 10 of the factor V gene were designed. A common upstream primer was paired with either a mutant or wild-type-specific downstream primer. The 3'-most nucleotide of the specific primers recognized either the mutant or normal allele, and the 3' penultimate nucleotide was mismatched to enhance specificity of the reaction. The assay was validated using authentic factor VLeiden DNA samples. Seven of 103 hematologically normal children (6.8%) were found to be heterozygotes. Among 27 patients studied by the rAPC assay, ARMS assay and rAPC results were concordant in 26. Among these were a 1-year-old child with a calcified clot in the inferior vena cava. Both the patient and his father were heterozygous for the mutation and both had abnormal rAPC assays. rAPC and factor VLeiden assays were discordant in a young girl with a history of stroke. Biochemical rAPC assay was abnormal, while ARMS assay revealed amplification only with wild-type primers, suggesting a non-[R506Q] mechanism for rAPC. This assay will be a valuable tool for studying subjects with thromboses and their family members.