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K. El Karoui et al.
senting with aHUS, complement-mediated aHUS is pro- totypical of disease and occurs as a consequence of hered- itary or acquired complement abnormalities. Eculizumab, a monoclonal anti-C5 antibody that blocks the formation of C5b-9 complexes on the surface of endothelial cells, has revolutionized the care of patients with aHUS.4 However, in 30-40% aHUS patients the cause is ill- defined and the role of additional genetic or environmen- tal factors remains debatable.1
A major complication of HUS is high blood pressure flares related to renal microvascular thromboses and acti- vation of the renin-angiotensin system. Recently, a new concept termed hypertensive emergency (HE) has been introduced to better characterize the syndrome of acute onset high blood pressure with end-organ damage.5,6 HE is defined by severe elevation of systolic or diastolic blood pressure (>180 mmHg or 120 mmHg, respectively), associated with progressive organ dysfunction, such as neurological changes, left ventricular failure, or aortic dis- section. HE-associated kidney involvement includes renal failure with mechanical hemolytic anemia mimicking aHUS flares.1,3,5–8 This latter situation raises the issue of whether primary HUS is complicated by secondary HE, or primary HE leads to secondary HUS.
Whether HE-associated HUS is a complement-mediat- ed disease remains debated. The percentage of patients with HE is rarely reported in aHUS cohorts.4,9 In a recent study, no pathogenic or likely pathogenic variants were identified in 100 non-elderly patients presenting with severe hypertension, renal failure and a kidney biopsy showing arteriolar thrombotic microangiopathy.10 However, in a large study of 273 patients with aHUS, 14 patients (5%) also had hypertensive flares, with muta- tions affecting the regulation of the alternative comple- ment pathway in 2/14.11 Moreover, a recent case series reported that 8/17 patients with ‘hypertension-associated thrombotic microangiopathy’ carried a pathogenic vari- ant in the genes for complement factor H (CFH), comple- ment factor I (CFI), membrane cofactor protein (MCP) or complement component 3 (C3).12
In the current study, in a large French cohort we ana- lyzed the clinical, biological and genetic characteristics of patients with aHUS and HE at onset (HE-aHUS), and compared the findings with those of aHUS patients with- out HE (noHE-aHUS). We showed that patients with HE- aHUS have specific clinico-biological characteristics com- pared to those of patients without HE.
Methods
Patients
HUS was defined by renal involvement (acute renal failure or proteinuria) with mechanical hemolytic anemia (including low hemoglobin, elevated lactate dehydrogenase, and/or the pres- ence of schistocytes) and/or thrombocytopenia. Between 2000 and 2016, we screened 405 patients with adult-onset HUS and ADAMTS-13 activity >15% for complement function and genetic abnormalities. To retrospectively develop this study and identify patients with or without HE and HUS, the patients’ medical records were reviewed and relevant clinical and biolog- ical data were collected. Patients without blood pressure data were excluded from this retrospective study.
For this study, the exclusion criteria were: (i) HUS with co- existing diseases (such as infection-induced HUS, monoclonal
gammopathy, solid-organ transplantation, hematopoietic stem cell transplantation or malignancy) or (ii) lack of reliable blood pressure data. We adopted the term aHUS to define HUS with- out co-existing diseases.
HE was defined according to the 2013 European Society of Hypertension/European Society of Cardiology guidelines (sys- tolic blood pressure ≥180 mmHg and/or diastolic blood pressure >120 mmHg), together with end-organ damage, such as renal, neurological, cardiac or ophthalmological involvement.6 Blood pressure was measured repeatedly during the initial diagnosis. Neurological involvement included acute onset severe headache, confusion, seizures, cerebral infarction/hematoma, and cerebral magnetic resonance images compatible with posterior reversible encephalopathy syndrome (PRES). Cardiac involvement included acute left or right ventricular dysfunction and cardiac arrythmia.
HE-aHUS and noHE-aHUS were defined as aHUS with or without HE, respectively. This study includes patients previous- ly reported by van der Born et al.8 We retrospectively found that ten patients published as having aHUS in 2013 had HE-aHUS at onset.9
Complement analyses
Complement evaluation and genetic analyses were performed as part of the usual work-up of patients diagnosed with aHUS. Plasma concentrations of C3, C4, factor B, factor H and factor I, and MCP expression on granulocytes were quantified as previ- ously described.9 All coding sequences of the CFH, CFI, MCP, C3, complement factor B (CFB) and thrombomodulin (THBD) genes were analyzed by direct sequencing as previously described or by next-generation sequencing.13 In our study, we defined a variant as rare when its minor allele frequency was below 1% in the general population. Among these rare variants, we named as pathogenic those for which the genetic change affects protein function (well-established in vitro functional stud- ies supportive of a damaging effect on the gene product), and/or the genetic change was found in a disease-related functional domain, and/or affects protein expression (nonsense, frameshift, canonical +/- one or two splice sites variants, well-demonstrated lack of in vitro synthesis, or quantitative deficiency in the patient’s plasma) (definitions adapted from Richards et al.14 and Goodship et al.15). The other variants were classified as variants of uncertain significance.
All patients gave informed consent for genetic analyses. The study was approved by the ethics committee of the French national clinical research projects authority (number AOM08198). DNA samples available from 80 healthy blood donors were also sequenced for the same genes.
Statistical analyses
Data are presented as percentages or mean ± standard devia- tion. The Fisher exact test was used to compare qualitative data. Renal survival was analyzed with Kaplan-Meier estimates and the log-rank test or by univariate and multivariate Cox propor- tional hazards regression when indicated. A P value <0.05 was considered statistically significant.
Results
Clinical and biological characteristics of atypical hemolytic uremic syndrome patients with or without hypertensive emergency
Of 405 HUS patients, 142 were excluded because of co- existing disease, and 126 had no blood pressure data. Thus, 137 patients with aHUS were enrolled in this study.
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haematologica | 2019; 104(12)