May 2026 Research Update

This month added clearer signals that the best-known treatments for aHUS do not act the same way across all aHUS subtypes. A review focused on anti-factor H antibody aHUS found faster improvement in blood findings with plasma exchange than with eculizumab, while kidney recovery timing looked similar between approaches. Individual case reports then highlighted why the underlying cause matters: some situations looked compatible with complement overactivation responding to C5 blockers, while others (such as DGKE-related disease) did not clearly fit that pattern. [1] [2] [3] [4]

In the systematic review of 99 people with anti-factor H antibody aHUS and native kidneys, hematologic remission (improvement in the blood cell breakdown and platelet problems) happened sooner with plasma exchange than with eculizumab (median 9 vs 20 days). Time to kidney recovery looked similar (median 16 vs 20 days), and differences in later chronic kidney disease or death were not statistically clear, partly because the two groups differed at baseline and the overall evidence was limited. For patients, this helps explain why some centers still use plasma exchange in this specific antibody-driven form, even in the era of complement blockers. [1]

Several case reports described situations where eculizumab appeared to align with improvement in kidney function and blood markers, but these are single-patient observations and do not prove cause and effect. This included a thrombotic microangiopathy after ingesting a large amount of avermectin with high C5b-9 (a marker of terminal complement activation), where kidney function and blood findings improved after eculizumab, and eculizumab was later stopped. Another case described complement-mediated thrombotic microangiopathy presenting with malignant hypertension and an unusual pancreatic mass that resolved during eculizumab, followed by relapse after stopping. [4] [3]

Not all genetically linked aHUS behaves as a complement-driven illness, and one pediatric report emphasized that mismatch. In a child with a homozygous DGKE mutation, complement levels stayed normal and relapses were described as proteinuria during treatment interruptions, leading the authors to argue that eculizumab was not addressing the main disease driver. The case also illustrates a real-world issue: when genetic confirmation is delayed, people may receive complement blockers before it is clear whether the disease mechanism fits. [2]

For patients and caregivers, the main message is that aHUS is a group of conditions that can look similar but may need different approaches depending on the cause (for example, anti-factor H antibodies versus DGKE changes versus other complement gene variants). The strongest human evidence this month came from a review in anti-factor H antibody aHUS, where plasma exchange was linked to faster blood recovery than eculizumab, while kidney recovery time looked similar. The other treatment signals were from case reports, which can highlight possibilities (including relapse after stopping complement blockers in one case) but cannot predict what will happen for most people. [1] [3] [2]

What remains uncertain is how much of the differences between treatments in the review were due to people starting therapy at different stages of illness, and how well the case report experiences apply to others with similar gene findings. What became clearer this month is the practical importance of identifying the aHUS subtype when possible, because some reported courses fit a complement-activation story while others did not. This is mainly an update to understanding rather than a change that applies uniformly to all patients right now. [1] [4] [3] [2]

This month underscored that aHUS can be triggered by very different real-life situations, and that the surrounding risks can be as important as the kidney and blood problems themselves. Case reports described aHUS in settings such as pregnancy or postpartum illness, severe infections, and after kidney transplant, showing how varied the first signs can be. A separate safety-database analysis in ovarian cancer flagged reports of thrombotic microangiopathy conditions including atypical HUS during bevacizumab treatment, reminding readers that some medications can be linked to aHUS-like syndromes in routine reporting systems. Together, these studies add to the picture that aHUS is not one single storyline, and careful attention to triggers and complications remains central. [5] [6] [7] [8] [9]

Several reports focused on pregnancy-related and postpartum aHUS, but with different underlying biology. One pregnancy-associated case involved beta-thalassemia plus a CFH mutation, with initial plasmapheresis and dialysis followed by eculizumab, and later stabilization reported during follow-up. Another postpartum case described HELLP followed by aHUS, a novel CFHR5 deletion producing a truncated protein, abnormal C5b-9 formation in endothelial-cell tests, and recovery after plasma infusion and supportive care. [5] [6]

Infection-associated aHUS was described in two very different contexts: severe leptospirosis and post-transplant adenovirus. In the leptospirosis case, plasma exchange was used alongside antibiotics, steroids, and supportive care, with gradual improvement but dialysis dependence at discharge. In the kidney transplant case, ravulizumab (a longer-acting C5 inhibitor) was followed by improvement in fever, inflammatory markers, blood counts, and graft function, with regression of lung findings on imaging. [7] [8]

A key safety reminder came from a report of meningococcal meningitis during ravulizumab treatment in a teenager with anti-factor H antibodies, despite complete meningococcal vaccination and antibiotic prophylaxis. The child recovered with intravenous antibiotics, and no aHUS relapse was described during the hospitalization, but the case illustrates that "breakthrough" meningococcal infection can still occur with C5 inhibitors. In parallel, a pharmacovigilance study using FAERS reports in ovarian cancer identified safety signals for several blood-related side effects with bevacizumab and also noted that thrombotic thrombocytopenic purpura and atypical HUS were among serious events reported but not listed on the label, with a median time-to-onset of 30 days for hematologic events in that dataset. [10] [9]

For patients, these studies mainly add context for why aHUS episodes can happen around major body stresses such as pregnancy, infections, or transplant, and why people may have very different symptoms at the start. They also add a clear cautionary data point that serious meningococcal infection can still happen during C5 inhibitor therapy even with vaccination and preventive antibiotics, based on a single reported case. The bevacizumab safety study is not about people with known aHUS, but it adds to awareness that some cancer drugs have been linked to reports of aHUS-like syndromes in routine safety reporting. [10] [9]

What remains uncertain is how often these reported situations occur, because case reports and spontaneous safety reports cannot provide reliable rates or prove direct cause. What became clearer this month is the range of triggers and complications that have been documented, including infection risk during complement blockade and postpartum cases tied to specific complement-related gene changes. This information may matter now mainly for understanding and informed conversations, while stronger conclusions require larger studies. [5] [6] [7] [8] [10] [9]

This month strengthened the idea that identifying the underlying biology of aHUS is becoming more practical, while also showing why results can be complex. A laboratory study validated a droplet digital PCR test that matched an established method for detecting large CFHR gene deletions, which are relevant to aHUS risk in some people. Case-based genetic reports showed that similar-looking clotting-and-anemia syndromes can come from different inherited changes, even within one family. Preclinical mouse research then pointed to properdin (a complement pathway helper protein) as another possible drug target beyond C5, at least in a model driven by abnormal complement activity. [11] [12] [13]

In the testing study, droplet digital PCR results were fully concordant with MLPA across 41 DNA samples for detecting copy-number changes in CFHR1, CFHR3, and CFHR4, including homozygous CFHR1/CFHR3 deletions. This matters because it supports another way laboratories might measure these deletions reliably, although the authors noted that more work is needed to tell full versus partial deletions apart and to confirm clinical value in real diagnostic pathways. [11]

A case series of two brothers illustrated that genetics can point in more than one direction when thrombotic microangiopathy is suspected. Whole-exome sequencing identified a homozygous ADAMTS13 mutation linked to hereditary TTP and a homozygous CFHR1/CFHR3 deletion linked to aHUS, alongside very different clinical pictures between siblings (one with severe kidney involvement needing dialysis and plasma exchange, one mainly with blood count problems responding to plasma transfusion). For families, this reinforces why comprehensive genetic workups can clarify what condition is present when symptoms overlap. [12]

In a mouse model with a C3 gain-of-function change, complete properdin deficiency protected against kidney thrombotic microangiopathy and reduced complement activation, and an anti-properdin antibody given after disease onset prevented progression and improved kidney measures in that model. This is laboratory and animal work, so it does not predict patient outcomes, but it expands the set of complement targets researchers are testing beyond C5 inhibitors. The study also noted potential complications such as immune reactions to the antibody format and some long-term kidney changes in certain mice, which are part of early-stage drug development. [13]

For patients, this set of studies mainly affects understanding and future research rather than immediate changes in care. The ddPCR validation supports the idea that genetic risk factors like CFHR deletions may become easier to detect in some laboratory settings, which could help clarify subtype in certain situations. The sibling case series shows that similar symptoms can hide more than one inherited problem, which may help explain why doctors sometimes pursue broader genetic testing when thrombotic microangiopathy is unclear. [11] [12]

What remains uncertain is how widely the new ddPCR approach will be adopted and whether it will improve outcomes compared with existing testing workflows. The properdin work is an early signal from mice that other complement-blocking strategies might be possible in the future, but it is not yet a human treatment result. Taken together, these studies clarify that aHUS is increasingly being divided into more precise biological subtypes, which is important groundwork for more tailored research. [11] [13]