Congenital thrombotic thrombocytopenic purpura related to a novel mutation in ADAMTS13 gene and management during pregnancy
Authors: Narendranath Epperla, Kathleen Hemauer, Kenneth D. Friedman, James N. George, Patrick Foy
Journal: American Journal of Hematology (2016)

A 19-year-old G2P0010 Caucasian female was hospitalized at 29 weeks gestation with acute change in vision of her left eye. She reported progressive swelling of her face and bilateral lower extremities, nausea, and vomiting for 1 week prior to presentation. Three days prior to presentation, she developed blurred vision in the central part of her left eye. She denied any hemorrhagic diarrhea or abdominal pain prior to presentation. On initial assessment, the patient was noted to have elevated blood pressure (150/103) without tachycardia or hypoxia. Physical examination was remarkable for 1+ bilateral lower extremity edema with no focal neurological deficits. Slit lamp examination revealed multiple serous detachments of posterior pole of the left macula and small intra-retinal hemorrhage. Initial lab work was notable for severe anemia (hemoglobin [Hb] 6.7 g/dL), thrombocytopenia (platelets [PLT] 13 × 103/µL), elevated serum creatinine (1.45 mg/dL, reference range 0.5–1.1 mg/dL), and significant proteinuria (3+ on urinalysis). Laboratory data was consistent with hemolytic anemia (elevated LDH [1159 U/L], absolute reticulocyte count [296,000 cell/µL], indirect bilirubin [1.5 mg/dL], and decreased haptoglobin [<10 mg/dL]) (Table 1). Review of the peripheral blood smear demonstrated the presence of 2–3 schistocytes/HPF and thrombocytopenia suggestive of microangiopathy. aPTT, PT/INR and fibrinogen were normal, and direct antiglobulin test was negative. ADAMTS 13 activity was sent. Intrauterine fetal demise was documented through absence of fetal heart tones on abdominal ultrasound. The patient's presentation was consistent with thrombotic microangiopathy (TMA); and differential diagnosis included pre-eclampsia/eclampsia, hemolysis with elevated liver enzymes and low platelets (HELLP syndrome), atypical hemolytic uremic syndrome (aHUS), or thrombotic thrombocytopenic purpura (TTP). TTP is an acute, uncommon and potentially life-threatening multisystem disorder wherein patients present with thrombocytopenia, microangiopathic hemolytic anemia (MAHA), and clinical consequences of microvascular thrombi 1, 2. Most acute cases are acquired via IgG autoantibodies against the von Willebrand multimer cleaving metalloprotease, ADAMTS13. Confirmatory testing includes decreased ADAMTS13 activity and identification of ADAMTS13 inhibitory antibodies. She was transfused 2 units (U) of packed red blood cells, 1 U of apheresis donor platelets and plasma (2 U every 4 hr for a total of 4 U). Due to the concern for pre-eclampsia/eclampsia, she was started on magnesium therapy (4 g intravenous bolus, followed by 1 g/hr). Treatment led to improvement in hemolytic markers and platelet count. On hospital day 2, she underwent induction of labor followed by dilation and curettage. Following the evacuation of fetal products, her Hb, PLT, and markers of hemolysis improved (Table 1). In addition, there was improvement in her neurologic symptoms (blurry vision) and renal function (serum creatinine). Three days postpartum, she developed recurrent laboratory evidence of microangiopathy (Table 1). ADAMTS13 activity measured by fluorescence resonance energy transfer (FRET)-based kinetic assay returned at 7% (normal activity >67%) with no detectable inhibitory antibody by mixing study and no detectable autoantibody by serologic assay. The patient was diagnosed as having TTP, and ADAMTS13 gene sequence tests were sent to explore the possibility of congenital ADAMTS13 deficiency (cTTP). Congenital TTP (cTTP) usually manifests in neonates and children, but can present in adulthood in certain situations such as pregnancy 3, 4. Diagnosis of cTTP requires identification of the clinical syndrome of microangiopathy, low ADAMTS13 activity and the absence of an inhibitory or clearing autoantibody. Multiple mutations in the ADAMTS13 protein have been described 5. She was transferred to the intensive care unit for emergent plasma exchange (PLEX). She had daily PLEX (50 cc/kg for the first 2 procedures, and 40 cc/kg for the next two procedures, with plasma as the replacement product) with improvement in her clinical status and hemolytic markers after the fourth cycle of PLEX. She was subsequently discharged home in stable condition and was noted to have normal counts in the outpatient clinic visits. PCR amplification and bidirectional DNA sequence analysis of the complete coding region and splice junctions of each of the 29 exons of the ADAMTS13 was performed and compared to the reference sequence (NC_000009.11). Two sequence variations in the ADAMTS13 gene, c.3178T > C (p. R1060W) in the TSP7 domain and c.1297T > C (p.C433R) in the TSP1 domain of ADAMTS13, confirmed the diagnosis of cTTP. This 19 year-old female had pregnancy-associated onset of cTTP. Pregnancy-associated onset of cTTP has been previously associated with the exon 24 missense mutation, c.3178C > T 6. However, in our case, the patient had 2 sequence variations in the ADAMTS13 gene, c.3178T > C (p. R1060W) and c.1297T > C (p.C433R), a novel mutation that has not been previously described. This novel sequence has not been reported by the 1000 Genomes Project and is not listed by the Exome Aggregation Consortium or the Exome Sequencing Project databases. Twelve months later, the patient became pregnant. Due to the history of congenital TTP exacerbated by previous pregnancy, prophylactic plasma infusions (PI) were initiated at 6 weeks gestation, with a plan to maintain ADAMTS13 level of >10%. The patient was closely monitored weekly for signs of hemolysis, proteinuria, or pre-eclampsia with periodic monitoring of platelet count and ADAMTS 13. To maintain ADAMTS13 trough levels at goal, PI was increased to 20 cc/kg weekly at 20 weeks gestation and subsequently to 15 cc/kg two times per week at 32 weeks gestation (Fig. 1). She tolerated PI well throughout her pregnancy. She was administered 15 cc/kg of PI prior to induction and delivered a healthy newborn via vaginal delivery at 37 weeks gestation. PI's were continued weekly (at 15 cc/kg) for 4 weeks postpartum. Throughout the pregnancy and postpartum period, there was no thrombocytopenia or microangiopathic hemolysis. ADAMTS13 activity and platelet count during Pregnancy. ADAMTS13 activity and platelet count during Pregnancy ADAMTS13 was measured immediately before PI. Letters indicate the periods at which the dose of PI administered was increased to the next tier. A = 15 mg/kg PI every 2 weeks, B = 20 mg/kg PI every 2 weeks, C = 20 mg/kg PI every week, D = 15 mg/kg PI every weekly, and E = 15 mg/kg PI once prior to induction of labor. ADAMTS13 activity levels <5% were depicted as “0.”. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.] The patient's subsequent pregnancy was successfully managed with regular PI titrated to keep ADAMTS13 activity above 10% of control. The importance of PI prophylaxis during pregnancy for women with cTTP is emphasized by the report of two sisters who died with their first episodes of TTP during their first pregnancies, in the era before the cause and proper care of these patients was known 7. TTP is one of the thrombotic microangiopathic disorders characterized by erythrocyte destruction, widespread microvascular platelet aggregation, and organ dysfunction. Acquired TTP is a rare disorder, with an incidence of 2.2 cases per million per year 8. It is estimated that the incidence of cTTP may be only 5% of acquired TTP 9. However, among women who present with TTP during pregnancy, congenital forms may account for as many as 25% of patients 4. Historically, TTP was diagnosed based on the pentad of clinical features that included MAHA, thrombocytopenia, neurologic and renal abnormalities, and fever 10. However, at the present time (after the advent of PLEX and improved physician awareness of the diagnosis), the dyad of otherwise unexplained MAHA and thrombocytopenia accompanied by observation of ADAMTS13 activity of < 10% is sufficient to establish a diagnosis and initiate treatment. Acute TTP may be precipitated by pregnancy, and in all cases of pregnancy-associated TMA, TTP should be excluded. Subsequent pregnancies in persons with previous pregnancy-associated TTP have been associated with TTP recurrence, preeclampsia, and eclampsia 11. This is consistent with our patient's initial pregnancy, when she met diagnostic criteria for preeclampsia as well as for TTP 12. It is important to differentiate congenital from acquired TTP in pregnancy to guide appropriate therapy 6. With either congenital or acquired TTP, the outcome of pregnancy is closely related to the gestational age at presentation. In both congenital and acquired TTP, the outcome of index pregnancy is worse when symptoms of TTP begin before 30 weeks gestation. Good maternal and neonatal clinical outcomes have been reported in subsequent pregnancies following previous episodes of pregnancy associated congenital and acquired TTP. Favorable outcomes have been associated with close clinical monitoring and initiation of ADAMTS13 replacement therapy before 20 weeks of pregnancy, as they have been shown to prevent fetal loss and TTP occurrence 6, 13. The half-life of ADAMTS 13 has been estimated to be 2–3 days 14. It is quite interesting to note that the PI administered every 2 week intervals seem effective at maintaining ADAMTS13 activity above the threshold required to prevent TTP despite the 2–3 day half-life. Some authors have postulated that there could be an unknown mechanism of action or storage reservoir of infused ADAMTS13 that may prevent its breakdown and improve its availability 13. Nevertheless, the exact mechanism remains uncertain. Earlier studies have recommended regular PI in women with congenital TTP (cTTP) and subsequent pregnancies with titration of the dose based on the period of gestation and PLT counts 6. However, there are no guidelines with regard to the frequency of ADAMTS13 monitoring and dosing schedule of PI. We propose an algorithm for PI infusion (Fig. 2) starting at 6 weeks gestation and titrating the dose based on the ADAMTS13 activity to target a trough level of >10% throughout the pregnancy. This approach may minimize the risk of clinical complications of TTP that can occur during early stages of microvascular ischemia when thrombocytopenia may be mild or difficult to distinguish from other causes pregnancy-associated thrombocytopenia that occur in nearly 5% of all pregnancies 15. Like previous studies, we propose induction of labor between 36 and 38 weeks with administration of PI prior to induction and continuation of PI weekly for 4 weeks postpartum. Algorithm for treatment of congenital TTP with PI using ADAMTS13 levels. Proposed algorithm for PI for congenital thrombotic thrombocytopenia during pregnancy. PI = Plasma Infusion. Algorithm suggests initiation of plasma therapy at 7.5 cc/kg q 2 weeks with periodic monitoring of trough ADAMTS13 level. Increase dose of plasma to next tier when trough ADAMTS13 activity is <10% during gestation. Peripartum with or without plasma supplementation is also indicated. To our knowledge, this is the first reported case in the English literature wherein the management of subsequent pregnancy in cTTP was done with PI using monitoring of ADAMTS13 activity with favorable outcome.c.3178C > T mutation in exon 24 (p.R1060W) has been reported in adult onset cTTP 16, 17. This sequence variant was noted with higher frequency (17/23) in a cohort of women with cTTP enrolled in the United Kingdom TTP registry 6. Though this mutation has no effect on enzyme activity, it causes intracellular retention of ADAMTS13 (<5% secretion) 16. Studies comparing the age of onset of symptoms, the location of variations within the ADAMTS13 sequence, and the plasma level of ADAMTS13 activity as assessed by the exquisitely sensitive SELDI-TOF mass spectrometry method indicated that patients with sequence variation c.3178T > C (p.R1060W) had ADAMTS13 levels between 3 and 7% and tended to present later in life such as occurred in our case 18. In our patient, a second heterozygous mutation was identified, c.1297T > C (p.C433R). Heterozygous sequence variation c.1297T > C in exon 11 that changes Cysteine at codon 433 to Arginine (p.C433R) is a novel mutation and has not been previously reported. The exact significance of this novel mutation is unclear but cysteine 433 is highly conserved among species and multiple computational prediction algorithms (SIFT, PolyPhen2, SNPS&Go, and MutPred) suggest that this variation would be disease-causing. It is of paramount importance to diagnose cTTP during pregnancy and differentiate from its mimickers, including pre-eclampsia, eclampsia, HELLP syndrome, aHUS, and acquired TTP 19. Early institution of ADAMTS13 replacement therapy with PI is the key to a successful pregnancy outcome. We strongly advocate treatment with PI as soon as pregnancy is diagnosed. We suggest titration of the dose and interval of PI based on the ADAMTS13 activity to target a trough level of >10% throughout the pregnancy. However, close monitoring of hemolytic markers and platelet count may serve as a surrogate for measurements of ADAMTS13 activity if testing is not readily available.