Congenital Thrombotic Thrombocytopenic Purpura: A Rare Cause of Recurrent Thrombocytopenia and Anemia

Congenital thrombotic thrombocytopenic purpura (cTTP) is a rare autosomal recessive microangiopathic disorder caused by inherited mutations in the ADAMTS13 gene. cTTP treatment involves infusing ADAMTS13-rich blood products like fresh frozen plasma (FFP) to replenish levels and prevent disease relapses. Alternative therapies like recombinant ADAMTS13, plasma-derived Factor VIII, or caplacizumab may be used for patients unable to tolerate FFP. We present a case of a five-month-old girl who had recurrent episodes of anemia and thrombocytopenia. She was diagnosed with cTTP based on the presence of low ADAMTS13 activity and the identification of a homozygous likely pathogenic variant in the ADAMTS13 gene. After receiving regular transfusions of FFP, our patient improved significantly and has been asymptomatic for 18 months with no transfusion complications.

Clinical Manifestations, Current and Future Therapy, and Long-Term Outcomes in Congenital Thrombotic Thrombocytopenic Purpura

Congenital thrombotic thrombocytopenic purpura (cTTP) is an extremely rare disease characterized by the severe deficiency of a disintegrin and metalloproteinase with thrombospondin type 1 motifs 13 (ADAMTS13), caused by ADAMTS13 mutations. While ADAMTS13 supplementation by fresh frozen plasma (FFP) infusion immediately corrects platelet consumption and resolves thrombotic symptoms in acute episodes, FFP treatment can lead to intolerant allergic reactions and frequent hospital visits. Up to 70% of patients depend on regular FFP infusions to normalize their platelet counts and avoid systemic symptoms, including headache, fatigue, and weakness. The remaining patients do not receive regular FFP infusions, mainly because their platelet counts are maintained within the normal range or because they are symptom-free without FFP infusions. However, the target peak and trough levels of ADAMTS13 to prevent long-term comorbidity with prophylactic FFP and the necessity of treating FFP-independent patients in terms of long-term clinical outcomes are yet to be determined. Our recent study suggests that the current volumes of FFP infusions are insufficient to prevent frequent thrombotic events and long-term ischemic organ damage. This review focuses on the current management of cTTP and its associated issues, followed by the importance of upcoming recombinant ADAMTS13 therapy.

In vitro characterization of a novel Arg102 mutation in the ADAMTS13 metalloprotease domain

BACKGROUND

Congenital thrombotic thrombocytopenic purpura is caused by defects in the ADAMTS13 gene. ADAMTS13 is normally preactivated by conformational changes of the Metalloprotease (M) domain. Studying a novel congenital thrombotic thrombocytopenic purpura p.R102S mutation in the M domain, which results in undetectable ADAMTS13 activity in the patient, could help to explain the patients' phenotype and to elucidate the currently unclear mechanism of allosteric preactivation.

OBJECTIVES

To investigate the in vitro effect of p.R102S mutation on ADAMTS13 secretion, activity, and allosteric preactivation.

METHODS

Molecular modeling was used to study the effect of the mutation on the stability of ADAMTS13. Recombinant mutant ADAMTS13 was generated by transient and stable transfection of, respectively, CHO K1 and HEK293-T cells. ADAMTS13 antigen was measured in enzyme-linked immunosorbent assay. ADAMTS13 activity was measured in a FRETS-VWF73 assay. Allosteric preactivation was assessed in FRETS-VWF73 assay, using monoclonal antibody (mAb) 17G2 that normally induces a ∼2-fold increase in activity, and in enzyme-linked immunosorbent assay using mAb 6A6 recognizing a cryptic epitope in the M domain that becomes exposed after binding of 17G2.

RESULTS

p.R102S mutation destabilizes the interactions between the M and Disintegrin-like (D) domain. p.R102S mutant secretion was impaired (35% of wild type) and activity was severely reduced (12% of wild type). p.R102S mutant could still be activated and the cryptic epitope of 6A6 was still fully exposed by 17G2 addition.

CONCLUSION

p.R102S mutation destabilizes the M-D domain interactions, causing impaired ADAMTS13 secretion and activity, which explains the patients' phenotype. Allosteric preactivation of ADAMTS13 remains conserved in the presence of the p.R102S mutation.

[Recurrent thrombocytopenia with hemolytic anemia in a boy aged 3 years]

A boy, aged 3 years and 8 months, had recurrent thrombocytopenia with hemolytic anemia for more than 3 years. The physical examination showed no enlargement of the liver, spleen, and lymph nodes or finger deformities. Laboratory results showed a negative result of the direct antiglobulin test, normal coagulation function, and increases in bilirubin, lactate dehydrogenase and reticulocytes. The results of von Willebrand factor-cleaving protease ADAMTS13 activity assay showed extreme deficiency, and antibody assay showed negative ADAMTS13 inhibitory autoantibodies. Next-generation sequence showed compound heterozygous mutation in the ADAMTS13 gene. The boy was diagnosed with congenital thrombotic thrombocytopenic purpura. This disease may be easily misdiagnosed as Evans syndrome and is difficult to diagnose in clinical practice. The child had developed the disease since birth, but it took 3 years to make a confirmed diagnosis. Therefore, congenital thrombotic thrombocytopenic purpura should be considered for children with jaundice at birth, recurrent thrombocytopenia with hemolytic anemia, and negative results of the direct antiglobulin test. The detection of ADAMTS13 activity and ADAMTS13 inhibitory autoantibodies should be performed as soon as possible for a definite diagnosis, and gene detection should be performed to make a confirmed diagnosis when necessary.

Clinical Features and Gene Mutation Analysis of Congenital Thrombotic Thrombocytopenic Purpura in Neonates

Congenital thrombotic thrombocytopenic purpura (TTP) is a rare hereditary disease with a high mortality rate; however, improved patient survival is possible with prompt diagnosis and treatment. The clinical features and mutation sites of a disintegrin and metalloproteinase with thrombospondin motifs 13 (ADAMTS13) in congenital TTP were analyzed in a neonate with suspected congenital TTP. High-throughput sequencing, polymerase chain reaction, and Sanger sequencing were utilized for screening of genes related to thrombocytopenic diseases and ADAMTS13 gene mutation testing on blood samples from the neonate and the parents. Domestic and foreign literature reporting the clinical features and variants of ADAMTS13 in neonates with congenital TTP were retrieved, compared, and analyzed. The patient in this case was a girl who had been born for 1 h and admitted to the hospital due to "dyspnea for 1 h." Routine blood tests on admission revealed profound thrombocytopenia. She quickly developed symptoms of systemic hemorrhage and eventually died. The neonate had two older sisters who had died of idiopathic thrombocytopenia and hemorrhage within 24 h of birth. Genetic testing showed that the neonate harbored a compound heterozygous mutation in ADAMTS13, c.1187G>A/c.1595G>T, which is a novel variant. Of the 12 cases (1 case in China and 11 cases in other countries) of congenital TTP in neonates that have been reported globally, ADAMTS13 mutation analysis was only performed in eight neonates. Common clinical manifestations included dyspnea of unknown etiology, bruising, jaundice, hemorrhage, and thrombocytopenia. Hence, the current case contributes to our understanding of the clinical manifestations and types of variants in neonates with congenital TTP. Our results demonstrate the efficacy of high-throughput sequencing technology in genetic testing of neonates suspected with congenital TTP and have revealed a novel compound missense mutation in ADAMTS13 that has not been reported in China or elsewhere.

High prevalence of hereditary thrombotic thrombocytopenic purpura in central Norway: from clinical observation to evidence

Essentials The population prevalence of hereditary thrombotic thrombocytopenic purpura (TTP) is unknown. We studied the prevalence of hereditary TTP and population frequencies of two ADAMTS-13 mutations. A high frequency of hereditary TTP related to ADAMTS-13 mutation c.4143_4144dupA was found. Vicinity of ABO blood group and ADAMTS-13 loci may facilitate screening of ADAMTS-13 mutations.

SUMMARY

Background Hereditary thrombotic thrombocytopenic purpura (TTP) caused by ADAMTS-13 mutations is a rare, but serious condition. The prevalence is unknown, but it seems to be high in Norway. Objectives To identify all patients with hereditary TTP in central Norway and to investigate the prevalence of hereditary TTP and the population frequencies of two common ADAMTS-13 mutations. Patients/Methods Patients were identified in a cross-sectional study within the Central Norway Health Region by means of three different search strategies. Frequencies of ADAMTS-13 mutations, c.4143_4144dupA and c.3178 C>T (p.R1060W), were investigated in a population-based cohort (500 alleles) and in healthy blood donors (2104 alleles) by taking advantage of the close neighborhood of the ADAMTS-13 and ABO blood group gene loci. The observed prevalence of hereditary TTP was compared with the rates of ADAMTS-13 mutation carriers in different geographical regions. Results We identified 11 families with hereditary TTP in central Norway during the 10-year study period. The prevalence of hereditary TTP in central Norway was 16.7 × 10(-6) persons. The most prevalent mutation was c.4143_4144dupA, accounting for two-thirds of disease causing alleles among patients and having an allelic frequency of 0.33% in the central, 0.10% in the western, and 0.04% in the southeastern Norwegian population. The allelic frequency of c.3178 C>T (p.R1060W) in the population was even higher (0.3-1%), but this mutation was infrequent among patients, with no homozygous cases. Conclusions We found a high prevalence of hereditary TTP in central Norway and an apparently different penetrance of ADAMTS-13 mutations.