HELLP (hemolysis, elevated liver enzymes, and low platelet count) syndrome is serious for the mother and the offspring. HELLP occurs in 0.2-0.8% of pregnancies and in 70-80% of cases it coexists with preeclampsia (PE). This review concerns the pathogenetic mechanisms of HELLP syndrome with an emphasis on differences between HELLP and early onset PE. The syndromes show a familial tendency. A previous HELLP pregnancy is associated with an increased risk of HELLP as well as PE in subsequent pregnancies, indicating related etiologies. No single world-wide genetic cause for excessive risk of HELLP or PE has been identified. Combinations of multiple gene variants, each with a moderate risk, with contributing effects of maternal and environmental factors, are probable etiological mechanisms. Immunological maladaptation is the most probable trigger of the insult to the invading trophoblast. This insult occurs early in the first trimester, as indicated by marker molecules in maternal blood. The levels of fetal messenger RNAs in maternal blood at gestational weeks 15-20 are significantly more abnormal in HELLP than in PE, suggesting that the insult is more extensive in HELLP. High levels of HLA-DR in maternal blood in women with HELLP may suggest a similarity to the rejection reaction. In third trimester placentas, gene derangement is more extensive in HELLP. Anti-angiogenic factors released into maternal blood induce the maternal syndromes. Maternal blood levels of anti-angiogenic sFlt1 are similar, but endoglin and Fas Ligand levels are possibly higher in HELLP than in PE. These factors trigger the vascular endothelium, resulting in an enhanced inflammatory response which is stronger in HELLP. Activated coagulation and complement, with high levels of activated leucocytes, inflammatory cytokines, TNF-α, and active von Willebrand factor, induce thrombotic microangiopathy with platelet-fibrin thrombi in microvessels. The angiopathy results in consumption of circulating platelets, causes hemolysis in affected microvessels and reduces portal blood flow in the liver. Placental Fas Ligand damages hepatocytes, resulting in periportal necrosis. In about one half of women with HELLP, activation of coagulation factors and platelets precipitates disseminated intravascular coagulation, which in a minority becomes uncompensated and contributes to life-threatening multiorgan failure.Copyright © 2012 Elsevier Ireland Ltd. All rights reserved.

        血栓性微血管病（thrombotic microangiopathy，TMA）是一组以微血管栓塞为病理特征的疾病。主要表现为微血管病性溶血性贫血、血小板减少、微循环血小板血栓引起神经系统、肾脏等器官受累［1］。经典的血栓性微血管病主要指血栓性血小板减少性紫癜（TTP）和溶血性尿毒综合征（HUS）。TTP和HUS均有溶血及肾脏受累的症状，且血浆置换可取得较好的疗效，两者之间的鉴别诊断较为困难，其病理变化均为内皮细胞损伤、微血管内血栓形成。近年来也有学者提出将两种疾病合称为TTP-HUS综合征。浏览更多请关注本刊微信公众号及当期杂志。

Atypical hemolytic uremic syndrome (aHUS) is a type of thrombotic microangiopathy (TMA) defined by thrombocytopenia, microangiopathic hemolytic anemia, and renal failure. aHUS is caused by uncontrolled complement activation in the alternative pathway (AP). A variety of genetic defects in complement-related factors or acquired autoantibodies to the complement regulators have been found in 50 to 60% of all cases. Recently, however, the classification and diagnosis of aHUS are becoming more complicated. One reason for this is that some factors, which have not been regarded as complement-related factors, have been reported as predisposing factors for phenotypic aHUS. Given that genotype is highly correlated with the phenotype of aHUS, careful analysis of underlying genetic abnormalities or acquired factors is needed to predict the prognosis or to decide an optimal treatment for the disease. Another reason is that complement dysregulation in the AP have also been found in a part of other types of TMA such as transplantation-related TMA and pregnancy-related complication. Based on these findings, it is now time to redefine aHUS according to the genetic or acquired background of abnormalities.Here, we review the pathogeneses and the corresponding phenotypes of aHUS and complement-related TMAs.

\n Pregnancy-associated atypical hemolytic uremic syndrome (aHUS) is a life-threatening thrombotic microangiopathy which may be mistaken for hemolysis, elevated liver enzymes, and low platelet count (HELLP) syndrome. We sought to identify laboratory parameters that differentiate aHUS and HELLP syndrome in the postpartum period. PubMed was searched from inception to March 2018 to identify cases of aHUS in the postpartum period, while cases of HELLP syndrome were identified from a cohort of deliveries at our institution from January 2015 to December 2018. Postpartum laboratory data were abstracted as either peak values (AST [aspartate transaminase]; creatinine; LDH [lactate dehydrogenase]) or nadir values (hemoglobin; platelet count). Differences were compared using the\n t\n test, Wilcoxon Rank Sum, or χ\n 2\n test, and receiver operating characteristic (ROC) curve analyses were performed. We identified 46 cases of aHUS and 45 cases of HELLP syndrome in the postpartum period. Women with HELLP syndrome were older, but rates of nulliparity and cesarean delivery, and gestational age at delivery, were similar between groups. Peak serum creatinine and LDH values after delivery were the most useful to diagnose aHUS with area under the curve 0.996 (95% CI, 0.99–1.0) and 0.91 (95% CI, 0.83–0.98) respectively. Serum creatinine ≥1.9 mg/dL, LDH ≥1832 U/L, or serum creatinine ≥1.9 mg/dL in combination with LDH ≥600 U/L were the optimal thresholds for diagnosing pregnancy-associated aHUS. We conclude that standard laboratory data, most specifically peak serum creatinine and LDH, may be used to differentiate aHUS and HELLP syndrome in the postpartum period.\n

Atypical hemolytic uremic syndrome (aHUS), a rare variant of thrombotic microangiopathy, is characterized by microangiopathic hemolytic anemia, thrombocytopenia, and renal impairment. The condition is associated with poor clinical outcomes with high morbidity and mortality. Atypical HUS predominantly affects the kidneys but has the potential to cause multi‐organ system dysfunction. This uncommon disorder is caused by a genetic abnormality in the complement alternative pathway resulting in over‐activation of the complement system and formation of microvascular thrombi. Abnormalities of the complement pathway may be in the form of mutations in key complement genes or autoantibodies against specific complement factors. We discuss the pathophysiology, clinical manifestations, diagnosis, complications, and management of aHUS. We also review the efficacy and safety of the novel therapeutic agent, eculizumab, in aHUS, pregnancy‐associated aHUS, and aHUS in renal transplant patients.

The identification, characterization, and clinical observation of ADAMTS13 (a disintegrin and metalloprotease with thrombospondin-1-like domains) have provided important insights into the pathogenesis of thrombotic thrombocytopenic purpura (TTP). ADAMTS13 is a plasma enzyme essential for postsecretion proteolytic processing of von Willebrand factor (VWF). Absence of ADAMTS13 is associated with the occurrence of abnormally large multimers of VWF and is also associated with the occurrence of TTP. Initial assumptions that absent ADAMTS13 was itself the etiology of TTP have been tempered by subsequent observations that ADAMTS13 activity can be severely deficient without clinical abnormalities and that patients can have characteristic clinical features of TTP without severe ADAMTS13 deficiency. A current interpretation of these observations is that ADAMTS13 deficiency is a major risk factor for the development of TTP, but it is neither always necessary nor sufficient to cause TTP. This interpretation is consistent with other vascular and thrombotic disorders in which multiple risk factors and associated conditions contribute to the etiology of acute events.

Thrombotic thrombocytopenic purpura (TTP) is the common name for adults with microangiopathic hemolytic anemia, thrombocytopenia, with or without neurologic or renal abnormalities, and without another etiology; children without renal failure are also described as TTP. The diagnosis of TTP is an indication for plasma exchange treatment, but beginning treatment requires sufficient confidence in the diagnosis to justify the risk of plasma exchange complications. Documentation of a severe deficiency of plasma ADAMTS13 activity, defined as less than 10% of normal, is not essential for the diagnosis of TTP. Some patients without severe ADAMTS13 deficiency may benefit from plasma exchange treatment; in addition, some patients with severe ADAMTS13 deficiency may subsequently be diagnosed with another cause for their clinical features. However, severe acquired ADAMTS13 deficiency does define a subgroup of patients who appear to benefit from treatment with corticosteroids and other immunosuppressive agents in addition to plasma exchange but who have a high risk for relapse. Approximately 80% of patients survive their acute episode, a survival rate that has not changed since the introduction of plasma exchange treatment. Although recovery may appear to be complete, many patients have persistent minor cognitive abnormalities. More effective as well as safer treatment for TTP is needed.