Hemolytic Uremic Syndrome

Underlying Genetics of aHUS: Which Connection with Outcome and Treatment Discontinuation?

Atypical hemolytic uremic syndrome (aHUS) is a rare disease caused by a genetic dysregulation of the alternative complement pathway, characterized by thrombocytopenia, hemolytic anemia, and acute kidney injury, and included in the group of thrombotic microangiopathies. With the introduction of humanized monoclonal antibodies that inhibit C5 activation, the natural history of aHUS completely changed, with a better prognosis, a quick recovery of renal function, and a significant reduction of end-stage renal disease incidence. Nowadays, there is an increasing interest in the molecular and genetic bases of this severe disease. The aim of this narrative review is to provide readers with a practical guide about different possible involved genes, elucidating the specific role of each transcribed protein in the pathogenesis of aHUS. Moreover, we analyzed the main current evidence about the relationship among genetic mutations, outcomes, and the risk of recurrence of this manifold disease.

[Thrombotic microangiopathy]

In the emergency room, patients with anemia and thrombocytopenia are common. Although these findings can often be explained by the medical situation, thrombotic microangiopathy is an important differential diagnosis. In this case, occlusion of the smallest vessels consequently leads to functional impairment of the affected organs. Patients generally present with symptoms of organ dysfunction, e.g., in the kidney or brain. Characteristically, Coombs-negative fragmentation of erythrocytes with hemolysis occurs in the area of the occluded vessels. Lactate dehydrogenase levels are elevated, and platelets and haptoglobin are reduced. Differential diagnoses beyond thrombotic microangiopathy that should be considered are numerous and diverse in their pathophysiology. Rapid workup is needed, because sometimes a specific treatment must be initiated rapidly. For example, thrombotic thrombocytopenic purpura leads to death in about 90% of patients if left untreated. However, by reconstitution of the underlying deficiency of the so-called ADAMTS13 (a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13) by plasma separation, survival can be ensured in most cases. Complement-mediated hemolytic uremic syndrome should also be considered and, if suspected, treated with complement inhibition. In many cases, however, thrombotic microangiopathy reflects a disorder elsewhere and may be a manifestation of severe hypertension or a coagulation disorder, such as disseminated intravascular coagulation or antiphospholipid syndrome. It can also be observed as a consequence of drug therapies or metabolic derangement. Systemic workup is therefore necessary for rapid clarification of differential diagnoses.

Hemolytic Uremic Syndrome Associated with Norovirus Gastroenteritis: Case Report and Literature Review

A previously healthy 3-year-old girl was admitted with fever, nonbloody diarrhea, vomiting for 3 days, and oliguria. Physical examination showed fatigue, pale appearance, hypertension, and mild periorbital edema. Laboratory examinations revealed anemia, thrombocytopenia, acute kidney injury, high LDH, and low haptoglobin levels. Urinalysis showed proteinuria and hematuria. Schistocytes and helmet cells were detected in the peripheral blood smear. There were no electrolyte imbalance and hypocomplementemia. Direct Coombs and viral panel were negative. Blood, urine, throat, and stool cultures were negative. Norovirus GII was positive in stool PCR, while other diarrheal agents were negative. The patient was diagnosed with norovirus gastroenteritis-induced hemolytic uremic syndrome (HUS). Furosemide was started for oliguria and hypertension, and blood pressure was controlled with oral nifedipine. On the 12th day of hospitalization, he was discharged with fully recover. To date, norovirus-associated HUS has been reported in 5 cases. Two of these are adult cases and the other three and our case are pediatric patients. In this case report and literature review, we observed that norovirus can cause HUS, especially in children, with a milder course than other types of HUS. The reason why it is more complicated in adult cases may be the presence of an additional underlying kidney disease. Since it was detected coincidentally in 1 case in the literature, it may be useful to screen for mutations in the complement pathway that may cause aHUS, if possible, in diarrhea-associated HUS caused by norovirus agents, but it was not present in our case.