The long-term outcomes of atypical haemolytic uraemic syndrome: a national surveillance study

Kidney Transplant Outcomes in Patients with Atypical Hemolytic Uremic Syndrome

BACKGROUND

Atypical hemolytic uremic syndrome (aHUS) is a rare disorder with a high probability of recurrence after a kidney transplant and can adversely affect the graft outcome. Our objective was to assess the transplant outcome of patients with aHUS who had undergone a kidney transplant.

METHODS

We retrospectively included patients who had undergone a kidney transplant and been diagnosed with aHUS based on an anti-complement factor H (AFH) antibody level >100 AU/mL and the presence of a genetic abnormality in complement factor H (CHF) or CHF-related (CFHR) genes. Data were analyzed with descriptive statistics.

RESULTS

Among 47 patients with AFH antibody levels >100 AU/mL, 5 (10.6%) had undergone a kidney transplant. The mean age was 24.2 years, and all were male. Atypical hemolytic uremic syndrome was diagnosed before transplant in 4 (80.0%) cases, whereas 1 was diagnosed after transplant owing to disease recurrence in the transplanted graft. Genetic analysis of all cases revealed one or more abnormalities in CFH and CFHR genes 1 and 3. With an average of 5 sessions of plasma exchange and the use of rituximab in 4 cases, there was a reduction in the disease severity with no recurrences in the post-transplant period. At the latest follow-up of 223 days, the mean serum creatinine level was 1.89 mg/dL, indicating good graft function.

CONCLUSIONS

Among patients diagnosed with aHUS, the use of pre-transplant plasma exchange and rituximab can be beneficial in terms of preventing graft dysfunction and reducing disease recurrence in the post-transplant period.

Risk of Atypical HUS Among Family Members of Patients Carrying Complement Regulatory Gene Abnormality

Introduction

Atypical hemolytic uremic syndrome (aHUS) is mainly due to complement regulatory gene abnormalities with a dominant pattern but incomplete penetrance. Thus, healthy carriers can be identified in any family of aHUS patients, but it is unpredictable if they will eventually develop aHUS.

Methods

Patients are screened for 10 complement regulatory gene abnormalities and once a genetic alteration is identified, the search is extended to at-risk family members. The present cohort study includes 257 subjects from 71 families: 99 aHUS patients (71 index cases + 28 affected family members) and 158 healthy relatives with a documented complement gene abnormality.

Results

Fourteen families (19.7%) experienced multiple cases. Over a cumulative observation period of 7595 person-years, only 28 family members carrying gene mutations experienced aHUS (overall penetrance of 20%), leading to a disease rate of 3.69 events for 1000 person-years. The disease rate was 7.47 per 1000 person-years among siblings, 6.29 among offspring, 2.01 among parents, 1.84 among carriers of variants of uncertain significance, and 4.43 among carriers of causative variants.

Conclusions

The penetrance of aHUS seems a lot lower than previously reported. Moreover, the disease risk is higher in carriers of causative variants and is not equally distributed among generations: siblings and the offspring of patients have a much greater disease risk than parents. However, risk calculation may depend on variant classification that could change over time.

Epidemiology of Atypical Hemolytic Uremic Syndrome: A Systematic Literature Review

Atypical hemolytic uremic syndrome (aHUS) is a rare but severe disorder that frequently has a genetic component and results from the overactivation of the alternative complement pathway. As research moves toward improved diagnosis and therapy of aHUS, it will be important to better understand its epidemiology. Our objective was to conduct a systematic literature review to assess the incidence and prevalence estimates of aHUS globally. A comprehensive literature search was conducted in Embase and MEDLINE. Additionally, practice guidelines, databases of national/international organizations, and regulatory agencies were searched. From 2960 publications identified via MEDLINE and Embase, 105 publications were eligible for full-text screening, and a total of eight full-text articles met eligibility criteria for inclusion. Regional epidemiologic estimates were obtained for Europe and Oceania. Country-specific data were available for France, Norway, Australia, and Italy. Four of the identified studies reported on the prevalence of aHUS, prevalence in the age group of 20 years or younger was ranging from 2.2 to 9.4 per million population, while the only study that reported prevalence in all ages showed a prevalence of 4.9 per million population. Six studies reported on the incidence of aHUS, annual incidence in the age group of 20 years or younger was ranging from 0.26 to 0.75 per million population, and for all ages, annual incidence was ranging from 0.23 to 1.9 per million population. To our knowledge, this is the first systematic review conducted to provide a comprehensive overview of global incidence and prevalence estimates of aHUS. In general, incidence estimates were similar across all the studies; however, prevalence data were found to be more variable. Study limitations were related to inconsistencies in the definitions of aHUS between studies and also a dearth of epidemiological studies assessing incidence and prevalence of aHUS outside of Europe.

Eculizumab Dosing in Infants

Eculizumab is the therapy of choice for patients with atypical hemolytic uremic syndrome (aHUS). Dosing recommendations stem from two trials: one retrospective trial (19 children and 5 infants) and one prospective trial (22 patients and 5 infants). This case report highlights the need for more precise dosing recommendations in children, particularly in infants, and for smaller vials of the medication to facilitate more precise dosing. Such changes would ensure that adverse events are minimized and that the children with aHUS who are treated with eculizumab experience an optimal clinical response.

Atypical presentation of atypical haemolytic uraemic syndrome

A 17-year-old girl presented with fever, myalgia, vomiting for 1 month and oliguria and dyspnoea for 4 days. She was tachycardic,hypertensive, with pedal oedema and decreased breath sounds. She had high serum creatinine (3 mg/dL), anaemia, thrombocytopenia, leucocytosis and eosinophilia with schistocytes. Lactate dehydrogenase, transaminases were high , with low haptoglobin and high ferritin (5269 ng/mL). Complement C3/C4 and fibrinogen were normal. Urinalysis showed large blood and protein and stool studies were negative. Her ADAMTS13 (a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13) was normal. Kidney biopsy showed acute interstitial nephritis (AIN) in addition to thrombotic angiopathy. The differentials - haemolytic uraemic syndrome (HUS), thrombotic thrombocytopenia (TTP) and haemophagocytic lymphohistiocytosis (HLH) were ruled out. Her genetic testing was abnormal for large CFHR1-CFHR3 homozygous deletion and heterozygous missense variant in exon 2 of DGKE making the diagnosis of atypical HUS. She received eculizumab and was discharged on oral steroids for AIN and biweekly eculizumab infusions with excellent recovery.

Advances in our understanding of the pathogenesis of hemolytic uremic syndromes

Hemolytic uremic syndrome (HUS) is major global health care issue as it is the leading cause of acute kidney injury in children. It is a triad of acute kidney injury, microangiopathic hemolytic anemia, and thrombocytopenia. In recent years, major advances in our understanding of complement-driven inherited rare forms of HUS have been achieved. However, in children 90% of cases of HUS are associated with a Shiga toxin-producing enteric pathogen. The precise pathological mechanisms in this setting are yet to be elucidated. The purpose of this review is to discuss advances in our understanding of the pathophysiology underlying HUS and identify the key questions yet to be answered by the scientific community.

Haemolytic uraemic syndrome

Haemolytic uraemic syndrome is a form of thrombotic microangiopathy affecting predominantly the kidney and characterised by a triad of thrombocytopenia, mechanical haemolytic anaemia, and acute kidney injury. The term encompasses several disorders: shiga toxin-induced and pneumococcus-induced haemolytic uraemic syndrome, haemolytic uraemic syndrome associated with complement dysregulation or mutation of diacylglycerol kinase ɛ, haemolytic uraemic syndrome related to cobalamin C defect, and haemolytic uraemic syndrome secondary to a heterogeneous group of causes (infections, drugs, cancer, and systemic diseases). In the past two decades, experimental, genetic, and clinical studies have helped to decipher the pathophysiology of these various forms of haemolytic uraemic syndrome and undoubtedly improved diagnostic approaches. Moreover, a specific mechanism-based treatment has been made available for patients affected by atypical haemolytic uraemic syndrome due to complement dysregulation. Such treatment is, however, still absent for several other disease types, including shiga toxin-induced haemolytic uraemic syndrome.

Complement factor B mutation-associated aHUS and myocardial infarction

A 6-month-old female infant was referred with a 3-day history of low-grade fever, slight nasal congestion and rhinorrhoea. On admission, the clinical findings were unremarkable and she was discharged home. However, she became progressively more listless with a decreased urine output and was once again seen in the emergency department. Analytically she was found to have metabolic acidosis, hyperkalaemia, thrombocytopaenia, anaemia and schistocytes in the peripheral blood smear. Based on these findings, the diagnosis of haemolyticâ-uremic syndrome was made. A few hours postadmission, there was an abrupt clinical deterioration. She went into cardiorespiratory arrest and she was successfully resuscitated. An ST-segment elevation was noted on the ECG monitor and the troponin I levels were raised, suggesting myocardial infarction. Despite intensive supportive therapy, she went into refractory shock and died within 30 hours.

Long-term remission with eculizumab in atypical haemolytic uraemic syndrome

The understanding of the role of complement dysregulation in atypical haemolytic uraemic syndrome (aHUS) has led to major changes in therapeutic approaches and outcomes. Eculizumab is a humanized anti-C5 monoclonal antibody that inhibits the terminal complement pathway and has revolutionized the treatment and prognosis of aHUS. However, published reports to date have had relatively short-term follow-up. We report two paediatric cases of aHUS successfully treated with eculizumab longer than 6 years with no serious adverse events and preservation of renal function.