Atypical Hemolytic Uremic Syndrome

Mendelian MONDO:0016244 Pathograph 4 Hematologic Disease Renal Disease Complement Disorder

Atypical hemolytic-uremic syndrome (aHUS) is a complement-mediated thrombotic microangiopathy (TMA) characterized by the triad of microangiopathic hemolytic anemia, thrombocytopenia, and acute kidney injury. Unlike typical HUS caused by Shiga toxin-producing E. coli, aHUS results from dysregulation of the alternative complement pathway due to genetic mutations in complement regulators (CFH, CFI, MCP/CD46) or complement effectors (CFB, C3), or from autoantibodies against factor H. Uncontrolled complement activation on endothelial surfaces leads to endothelial injury, platelet activation, and microvascular thrombosis predominantly affecting the renal microvasculature. aHUS can present at any age, with approximately 60% of cases having an identifiable genetic cause. Without treatment, it carries high morbidity with progression to end-stage renal disease. The introduction of eculizumab, a monoclonal antibody targeting complement component C5, has transformed the prognosis.

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◆

Subtypes

CFH-Associated aHUS

Mutations in complement factor H (CFH), the main soluble regulator of the alternative pathway. Most common genetic form, accounting for ~25-30% of genetic aHUS. Often severe with high relapse rate and poor renal prognosis without complement inhibition.

MCP/CD46-Associated aHUS

Mutations in membrane cofactor protein (MCP/CD46), a transmembrane complement regulator. Generally milder course with better renal prognosis and higher spontaneous remission rate compared to CFH mutations.

CFI-Associated aHUS

Mutations in complement factor I (CFI), a serine protease that cleaves C3b and C4b with cofactor assistance. Variable penetrance and intermediate prognosis.

CFB-Associated aHUS (Gain-of-Function)

Gain-of-function mutations in complement factor B (CFB) that enhance C3 convertase activity. Rare, accounting for ~1-2% of genetic aHUS.

C3-Associated aHUS

Mutations in complement component C3 that impair regulation by factor H or MCP. Accounts for ~5-10% of genetic aHUS.

Anti-Factor H Antibody aHUS

Autoimmune form caused by IgG autoantibodies against complement factor H, frequently associated with homozygous deletion of CFHR1 and CFHR3. More common in children and adolescents. Responds to plasma exchange and immunosuppression in addition to complement inhibition.

⚙

Pathophysiology

Alternative Complement Pathway Dysregulation

The central mechanism of aHUS is loss of regulation of the alternative complement pathway on endothelial cell surfaces. Normally, complement factor H (CFH), membrane cofactor protein (MCP/CD46), and factor I (CFI) cooperate to inactivate C3b deposited on host cell surfaces. In aHUS, genetic mutations in these regulators or gain-of-function mutations in complement effectors (CFB, C3) lead to unchecked C3 convertase (C3bBb) activity and amplification loop activation on endothelial surfaces.

Glomerular Endothelial Cell link

Complement Activation, Alternative Pathway link ↑ INCREASED Regulation of Complement Activation link ↓ DECREASED

Downstream

MAC-Mediated Endothelial Activation Unchecked complement activation generates C5a and membrane attack complex on endothelial cells.

Show evidence (2 references)

PMID:39918340 SUPPORT Human Clinical

"Atypical hemolytic uremic syndrome (aHUS) is a rare cause of thrombotic microangiopathy (TMA) caused by the dysregulation of the alternative complement pathway."

This 2025 consensus statement confirms that aHUS is fundamentally caused by alternative complement pathway dysregulation.

PMID:25843230 SUPPORT Human Clinical

"Tremendous advances in our understanding of the thrombotic microangiopathies (TMAs) have revealed distinct disease mechanisms within this heterogeneous group of diseases."

This authoritative review by leading aHUS researchers documents the complement-mediated disease mechanisms underlying aHUS.

MAC-Mediated Endothelial Activation

Uncontrolled complement activation generates membrane attack complex (MAC/C5b-9) on endothelial cells, causing direct cell injury. Sublytic MAC deposition induces endothelial activation with upregulation of adhesion molecules, tissue factor expression, and loss of thrombomodulin. Injured endothelium releases von Willebrand factor (vWF) multimers and exposes subendothelial collagen.

Glomerular Endothelial Cell link

Complement Activation link ↑ INCREASED

Downstream

Platelet Aggregation and Microthrombus Formation VWF multimer release and subendothelial collagen exposure recruit and activate platelets on the damaged endothelial surface.

Show evidence (2 references)

PMID:40436118 SUPPORT Human Clinical

"The understanding of the role of the membrane attack complex in some TMAs has led to the introduction of pharmacologic inhibition of complement C5, which greatly improved prognosis."

Walsh & Kavanagh 2025 review confirms the central role of MAC in endothelial injury in aHUS and related TMAs.

PMID:34169200 SUPPORT Human Clinical

"Atypical hemolytic uremic syndrome (aHUS) is a rare, complex, multisystem disease of dysregulated complement activity, characterized by progressive thrombotic microangiopathy (TMA), acute kidney injury, and multiorgan dysfunction"

This clinical trial confirms aHUS is characterized by complement-driven progressive TMA with multiorgan dysfunction.

Platelet Aggregation and Microthrombus Formation

VWF multimers released from activated endothelium and exposed subendothelial collagen promote platelet adhesion and aggregation. Tissue factor expression on activated endothelium triggers the coagulation cascade, generating fibrin-platelet microthrombi in arterioles and capillaries, particularly in the glomerular microvasculature.

Platelet link Glomerular Endothelial Cell link

Platelet Activation link ↑ INCREASED

Downstream

Renal Microvascular Thrombosis Fibrin-platelet thrombi occlude glomerular capillaries and arterioles.

Show evidence (1 reference)

PMID:40436118 SUPPORT Human Clinical

"These all result in pathologic features of thrombotic microangiopathy (TMA), which cause endothelial damage and organ injury."

Confirms TMA pathology involves microthrombus formation causing endothelial damage and downstream organ injury.

Renal Microvascular Thrombosis

Fibrin-platelet thrombi occlude glomerular capillaries and arterioles, causing mechanical shearing of red blood cells (schistocyte formation), consumptive thrombocytopenia, and ischemic injury to renal parenchyma. Progressive thrombotic microangiopathy leads to acute kidney injury and, if untreated, irreversible renal damage with cortical necrosis and progression to end-stage renal disease.

Glomerular Endothelial Cell link Red Blood Cell link

Blood Coagulation link ↑ INCREASED

Show evidence (1 reference)

PMID:40436118 SUPPORT Human Clinical

"These all result in pathologic features of thrombotic microangiopathy (TMA), which cause endothelial damage and organ injury. TMAs manifest with a microangiopathic hemolytic anaemia, thrombocytopenia, and commonly acute kidney injury."

Confirms that TMA pathology causes the clinical triad of MAHA, thrombocytopenia, and AKI through endothelial damage.

⬡

Pathograph

Use the checkboxes to hide or show graph categories. Hover nodes for evidence and cross-linked metadata.

●

Phenotypes

Blood 1

Thrombocytopenia VERY_FREQUENT Thrombocytopenia (HP:0001873)

Show evidence (2 references)

PMID:39918340 SUPPORT Human Clinical

"The diagnosis of TMA is made clinically by the triad: microangiopathic hemolytic anemia, thrombocytopenia, and organ damage (mainly acute kidney injury)."

Thrombocytopenia is part of the defining diagnostic triad.

PMID:23738544 SUPPORT Human Clinical

"Eculizumab resulted in increases in the platelet count; in trial 1, the mean increase in the count from baseline to week 26 was 73×10(9) per liter (P<0.001)."

The Legendre NEJM 2013 eculizumab trial documents thrombocytopenia at baseline that improved with complement inhibition.

Cardiovascular 2

Hypertension FREQUENT Hypertension (HP:0000822)

Show evidence (1 reference)

PMID:23542698 SUPPORT Human Clinical

"Affected individuals present with aHUS before age 1 year, have persistent hypertension, hematuria and proteinuria"

Lemaire et al. document persistent hypertension as a clinical feature in DGKE-aHUS, and hypertension is common across all aHUS subtypes.

Stroke OCCASIONAL Stroke (HP:0001297)

Show evidence (1 reference)

PMID:29907460 SUPPORT Human Clinical

"extrarenal organ manifestations occur in 19%-38% of patients within six months of initial disease presentation (dependent on organ)"

Stroke is among the extrarenal TMA manifestations documented in the Global aHUS Registry.

Digestive 1

Diarrhea Diarrhea (HP:0002014)

Show evidence (1 reference)

PMID:29907460 SUPPORT Human Clinical

"extrarenal organ manifestations occur in 19%-38% of patients within six months of initial disease presentation (dependent on organ)"

GI manifestations including diarrhea are among the extrarenal organ involvement documented in the Global aHUS Registry.

Genitourinary 3

Acute Kidney Injury VERY_FREQUENT Acute kidney injury (HP:0001919)

Show evidence (1 reference)

PMID:23307876 SUPPORT Human Clinical

"progression to ESRD after the first aHUS episode was more frequent in adults (46% versus 16%; P<0.001)"

The French nationwide series documents that AKI progressing to ESRD occurs in 46% of adults and 16% of children after first episode.

Proteinuria FREQUENT Proteinuria (HP:0000093)

Show evidence (1 reference)

PMID:23542698 SUPPORT Human Clinical

"Affected individuals present with aHUS before age 1 year, have persistent hypertension, hematuria and proteinuria (sometimes in the nephrotic range)"

Proteinuria is documented as a persistent feature of aHUS.

Hematuria FREQUENT Hematuria (HP:0000790)

Show evidence (1 reference)

PMID:23542698 SUPPORT Human Clinical

"Affected individuals present with aHUS before age 1 year, have persistent hypertension, hematuria and proteinuria"

Hematuria is documented as a persistent feature of aHUS.

Nervous System 1

Seizures OCCASIONAL Seizure (HP:0001250)

Show evidence (1 reference)

PMID:29907460 SUPPORT Human Clinical

"extrarenal organ manifestations occur in 19%-38% of patients within six months of initial disease presentation (dependent on organ)"

The Global aHUS Registry documents that 19-38% of patients develop extrarenal organ involvement within 6 months, including neurological.

Other 4

Microangiopathic Hemolytic Anemia VERY_FREQUENT Microangiopathic hemolytic anemia (HP:0001937)

Show evidence (1 reference)

PMID:39918340 SUPPORT Human Clinical

"The diagnosis of TMA is made clinically by the triad: microangiopathic hemolytic anemia, thrombocytopenia, and organ damage (mainly acute kidney injury)."

Brazilian consensus confirms MAHA as part of the defining diagnostic triad.

Reduced Haptoglobin Reduced haptoglobin level (HP:0020181)

Show evidence (1 reference)

PMID:40436118 SUPPORT Human Clinical

"TMAs manifest with a microangiopathic hemolytic anaemia, thrombocytopenia, and commonly acute kidney injury."

MAHA inherently involves reduced haptoglobin as a laboratory marker of intravascular hemolysis.

Elevated Lactate Dehydrogenase Increased circulating lactate dehydrogenase concentration (HP:0025435)

Show evidence (1 reference)

PMID:34169200 SUPPORT Human Clinical

"Normalization of platelet count, serum lactate dehydrogenase (LDH), and hemoglobin observed in the 26-week initial evaluation period was sustained"

Elevated LDH at baseline is implied by its normalization with ravulizumab treatment, confirming it as a key laboratory marker.

Schistocytosis Schistocytosis (HP:0001981)

Show evidence (1 reference)

PMID:40436118 SUPPORT Human Clinical

"TMAs manifest with a microangiopathic hemolytic anaemia, thrombocytopenia, and commonly acute kidney injury."

Schistocytosis is the defining morphologic finding of MAHA in TMA.

🧬

Genetic Associations

CFH Mutations

Autosomal dominant

Show evidence (3 references)

PMID:23307876 SUPPORT Human Clinical

"Sixty-one percent of patients had mutations in their complement genes."

The French nationwide series confirms high frequency of complement gene mutations in aHUS, with CFH being the most common.

PMID:29907460 SUPPORT Human Clinical

"Patients with a Complement Factor H mutation had reduced ESRD-free survival, whereas Membrane Cofactor Protein mutation was associated with longer ESRD-free survival."

Global aHUS Registry data confirm that CFH mutations carry the worst renal prognosis among complement gene mutations.

CGGV:assertion_b0a234f8-1d8e-4a26-a76f-40219591c75c-2023-07-02T160000.000Z SUPPORT Other

ClinGen classifies the CFH-atypical hemolytic-uremic syndrome gene-disease relationship as definitive with semidominant inheritance.

MCP/CD46 Mutations

Autosomal dominant

Show evidence (3 references)

PMID:29907460 SUPPORT Human Clinical

"Membrane Cofactor Protein mutation was associated with longer ESRD-free survival."

MCP mutations are confirmed to have better renal prognosis than CFH mutations.

PMID:23307876 SUPPORT Human Clinical

"The frequency of relapse after 1 year was 92% in children with MCP-associated HUS and approximately 30% in all other subgroups."

MCP-aHUS is notable for high relapse rate (92%) in children but better overall renal outcome compared to CFH mutations.

CGGV:assertion_bddaec4f-9f57-41b7-81a4-2f6ff3fc5e7b-2024-06-27T160000.000Z SUPPORT Other

ClinGen classifies the CD46-atypical hemolytic-uremic syndrome gene-disease relationship as definitive with semidominant inheritance.

CFI Mutations

Autosomal dominant

Show evidence (2 references)

PMID:29907460 SUPPORT Human Clinical

"Complement Factor I and Membrane Cofactor Protein mutations were more common in patients with initial presentation as adults and children, respectively."

CFI mutations are documented to be more common in adult-onset aHUS.

CGGV:assertion_3a5fcd7c-0da5-4ba3-b0c6-2d40f985c418-2023-06-01T160000.000Z SUPPORT Other

ClinGen classifies the CFI-atypical hemolytic-uremic syndrome gene-disease relationship as definitive with autosomal dominant inheritance.

CFB Gain-of-Function Mutations

Autosomal dominant

Show evidence (1 reference)

PMID:23307876 SUPPORT Human Clinical

"Sixty-one percent of patients had mutations in their complement genes."

CFB is among the complement genes with identified mutations in this nationwide series.

C3 Mutations

Autosomal dominant

Show evidence (1 reference)

PMID:23307876 SUPPORT Human Clinical

"Sixty-one percent of patients had mutations in their complement genes."

C3 is among the complement genes with identified mutations.

CFHR1/CFHR3 Deletion with Anti-Factor H Antibodies

Autosomal recessive

Show evidence (2 references)

PMID:25917093 SUPPORT Human Clinical

"No homozygous deletions of the CFHR1 and CFHR3 genes, which are frequently associated with the anti-FH Ab in aHUS patients, were found in the GP patients."

Confirms that CFHR1/CFHR3 homozygous deletions are frequently associated with anti-factor H antibodies specifically in aHUS.

PMID:23307876 SUPPORT Human Clinical

"214 patients with aHUS were enrolled between 2000 and 2008 and screened for mutations in the six susceptibility factors for aHUS and for anti-factor H antibodies."

Anti-factor H antibodies are recognized as a key susceptibility factor in the French national aHUS registry.

DGKE Mutations

Autosomal recessive

Show evidence (2 references)

PMID:23542698 SUPPORT Human Clinical

"we identified recessive mutations in DGKE (encoding diacylglycerol kinase ɛ) that co-segregated with aHUS in nine unrelated kindreds, defining a distinctive Mendelian disease."

Landmark paper identifying DGKE as a cause of aHUS through a non-complement mechanism involving prothrombotic DAG signaling.

PMID:23542698 SUPPORT Human Clinical

"DGKE is found in endothelium, platelets and podocytes. Arachidonic acid-containing diacylglycerols (DAG) activate protein kinase C (PKC), which promotes thrombosis, and DGKE normally inactivates DAG signaling."

Establishes the prothrombotic mechanism whereby loss of DGKE leads to sustained DAG/PKC signaling in endothelial cells and platelets.

THBD Mutations

Autosomal dominant

Show evidence (1 reference)

PMID:29907460 SUPPORT Human Clinical

"Atypical hemolytic uremic syndrome (aHUS) is a rare, genetic, life-threatening disease. The Global aHUS Registry collects real-world data on the natural history of the disease."

The Global aHUS Registry screened 851 patients for complement gene mutations including THBD, documenting its role as a susceptibility gene.

💊

Treatments

Eculizumab

Action: Pharmacotherapy NCIT:C15986

Agent: eculizumab ↗

Humanized monoclonal antibody that binds complement component C5, preventing cleavage to C5a and C5b and blocking MAC formation. First-line treatment for aHUS that has transformed outcomes, with rapid hematologic response and renal function improvement.

Show evidence (3 references)

PMID:23738544 SUPPORT Human Clinical

"Eculizumab inhibited complement-mediated thrombotic microangiopathy and was associated with significant time-dependent improvement in renal function in patients with atypical hemolytic-uremic syndrome."

Landmark NEJM 2013 trial demonstrating eculizumab efficacy in aHUS with improvement in both hematologic parameters and renal function.

PMID:23738544 SUPPORT Human Clinical

"In trial 1, dialysis was discontinued in 4 of 5 patients. Earlier intervention with eculizumab was associated with significantly greater improvement in the estimated GFR."

Eculizumab enabled discontinuation of dialysis and earlier intervention was associated with better renal outcomes.

PMID:25859752 SUPPORT Human Clinical

"This advance facilitated the development of novel, rational treatment options targeting terminal complement activation, e.g., using an anti-C5 antibody (eculizumab)."

International consensus confirms eculizumab as the rational treatment targeting the underlying complement pathophysiology.

Ravulizumab

Action: Pharmacotherapy NCIT:C15986

Agent: ravulizumab ↗

Long-acting C5 inhibitor engineered from eculizumab with extended dosing interval (every 8 weeks vs every 2 weeks). Non-inferior efficacy with improved convenience.

Show evidence (1 reference)

PMID:34169200 SUPPORT Human Clinical

"This analysis reveals that ravulizumab administered every 8 weeks is efficacious with an acceptable safety profile for the long-term treatment of adults with aHUS and provides additional clinical benefit beyond 6 months of treatment."

Phase 3 trial demonstrates long-term efficacy and safety of ravulizumab with every-8-week dosing in adults with aHUS.

Iptacopan

Action: Pharmacotherapy NCIT:C15986

Agent: iptacopan ↗

Novel oral small-molecule inhibitor of complement factor B, targeting the alternative complement pathway at the level of C3 convertase (C3bBb), upstream of the C5 inhibition site targeted by eculizumab and ravulizumab. Under clinical investigation for aHUS following demonstrated efficacy in C3 glomerulopathy and paroxysmal nocturnal hemoglobinuria. Case reports document rescue use in complement-mediated TMA refractory to anti-C5 agents.

Show evidence (2 references)

PMID:40996634 SUPPORT Human Clinical

"Iptacopan/LNP023, a novel, orally administered C3 convertase inhibitor that has shown efficacy in C3 glomerulopathy and paroxysmal nocturnal haemoglobinuria, is going to be tested in patients with atypical haemolytic syndrome."

Case report documents iptacopan mechanism and its emerging role in complement-mediated TMA including aHUS refractory to anti-C5 therapy.

PMID:42133203 SUPPORT Human Clinical

"Trials on novel complement inhibitors, regenerative medicine, targeted therapy, and stem cell therapy may also improve future treatment options."

2026 review confirms that trials on novel complement inhibitors beyond eculizumab represent an emerging therapeutic frontier in aHUS management.

Plasma Exchange/Infusion

Historical first-line therapy before eculizumab. Plasma exchange removes mutant complement factors and autoantibodies while replacing functional complement regulators. Still used as bridging therapy and for anti-factor H antibody-mediated aHUS.

Show evidence (3 references)

PMID:23738544 SUPPORT Human Clinical

"Plasma exchange or infusion may transiently maintain normal levels of hematologic measures but does not treat the underlying systemic disease."

The NEJM trial background confirms plasma exchange as prior standard of care that provided only transient hematologic improvement.

PMID:39918340 SUPPORT Human Clinical

"patients were submitted to plasma therapy (plasma exchange and/or plasma infusion) and/or liver transplantation, procedures that are not free of serious complications and that do not address the underlying pathophysiology of the disease."

Confirms plasma therapy was used historically but has limitations as it does not address the underlying complement dysregulation.

PMID:42169153 SUPPORT Human Clinical

"A multidisciplinary approach, including therapeutic plasma exchange (TPE), was employed, resulting in gradual clinical improvement, although the patient remained dialysis-dependent at discharge."

Case report of secondary aHUS triggered by severe leptospirosis demonstrates therapeutic benefit of plasma exchange as rescue intervention for complement-mediated complications in systemic infection.

Renal Transplantation

Action: organ transplantation MAXO:0010039

For patients who progress to ESRD. Risk of disease recurrence in the transplanted kidney varies by genotype (high for CFH mutations, low for MCP mutations). Combined liver-kidney transplantation has been performed for CFH mutations to correct the source of mutant protein.

Show evidence (1 reference)

PMID:39918340 SUPPORT Human Clinical

"patients were submitted to plasma therapy (plasma exchange and/or plasma infusion) and/or liver transplantation, procedures that are not free of serious complications"

Brazilian consensus documents that liver transplantation (combined with kidney transplantation for CFH mutations) was used historically and remains a consideration for refractory cases.

Immunosuppression for Anti-Factor H Antibodies

Action: Pharmacotherapy NCIT:C15986

For autoimmune aHUS with anti-factor H antibodies, combination of plasma exchange with immunosuppressive therapy (mycophenolate mofetil, rituximab, or cyclophosphamide) to reduce antibody production.

Show evidence (1 reference)

PMID:25917093 SUPPORT Human Clinical

"Autoantibodies targeting factor H (FH), which is a main alternative complement pathway regulatory protein, have been well characterized in atypical hemolytic uremic syndrome (aHUS)"

Confirms anti-FH autoantibodies as a well-characterized pathogenic mechanism in aHUS, providing the rationale for immunosuppressive treatment to reduce antibody production.

🌍

Environmental Factors

Complement-Activating Triggers

In genetically predisposed individuals, disease episodes are frequently triggered by complement-activating events including infections (particularly upper respiratory, gastrointestinal, and systemic infections such as severe leptospirosis), pregnancy (especially postpartum), organ transplantation, certain medications (calcineurin inhibitors, oral contraceptives), and autoimmune conditions. Severe infections provoke systemic inflammation and endothelial injury that can activate the alternative complement pathway in susceptible carriers, precipitating secondary aHUS manifestations.

Show evidence (3 references)

PMID:25843230 SUPPORT Human Clinical

"we review the clinical characteristics; the genetic and acquired drivers of disease; the broad spectrum of environmental triggers; and current diagnosis and treatment options."

Nester et al. 2015 review specifically addresses the broad spectrum of environmental triggers in aHUS.

PMID:42169153 SUPPORT Human Clinical

"Despite early initiation of intravenous antibiotics, steroids, and supportive care, the patient's condition deteriorated with features suggestive of atypical hemolytic uremic syndrome (aHUS), myocarditis, acute respiratory distress syndrome (ARDS), and acute liver injury. Diagnostic findings..."

Case report of aHUS triggered as a secondary complication of severe leptospirosis in a previously healthy patient, demonstrating how systemic infection-driven inflammation and endothelial injury activate complement-mediated TMA in genetically susceptible individuals. Responds to therapeutic plasma exchange, confirming complement-mediated disease pathophysiology.

PMID:23307876 SUPPORT Human Clinical

"Onset of aHUS occurred as frequently during adulthood (58.4%) as during childhood (41.6%). The percentages of patients who developed the disease were 23%, 40%, 70%, and 98% by age 2, 18, 40, and 60 years, respectively."

The age distribution of aHUS onset, with disease developing throughout life, suggests ongoing susceptibility to environmental triggers in genetically predisposed individuals.

🔬

Biochemical Markers

Reduced C3 Levels (DECREASED)

Context: Low serum C3 due to consumption from chronic alternative pathway activation. Present in a subset of aHUS patients, particularly those with CFH, CFB, or C3 mutations. Normal C3 does not exclude aHUS.

Elevated Soluble C5b-9 (INCREASED)

Context: Elevated serum levels of the terminal complement complex (sC5b-9) indicate ongoing terminal complement activation and correlate with disease activity. Normalization with C5 inhibitor therapy correlates with clinical response.

{ }

Source YAML

click to show

name: Atypical Hemolytic Uremic Syndrome
creation_date: "2026-04-22T12:00:00Z"
updated_date: "2026-05-16T00:00:00Z"
category: Mendelian
parents:
- Hematologic Disease
- Renal Disease
- Complement Disorder
disease_term:
  preferred_term: Atypical Hemolytic-Uremic Syndrome
  term:
    id: MONDO:0016244
    label: atypical hemolytic-uremic syndrome
description: >-
  Atypical hemolytic-uremic syndrome (aHUS) is a complement-mediated thrombotic
  microangiopathy (TMA) characterized by the triad of microangiopathic hemolytic
  anemia, thrombocytopenia, and acute kidney injury. Unlike typical HUS caused by
  Shiga toxin-producing E. coli, aHUS results from dysregulation of the alternative
  complement pathway due to genetic mutations in complement regulators (CFH, CFI,
  MCP/CD46)
  or complement effectors (CFB, C3), or from autoantibodies against factor H. Uncontrolled
  complement activation on endothelial surfaces leads to endothelial injury, platelet
  activation, and microvascular thrombosis predominantly affecting the renal
  microvasculature. aHUS can present at any age, with approximately 60% of cases having
  an identifiable genetic cause. Without treatment, it carries high morbidity with
  progression to end-stage renal disease. The introduction of eculizumab, a monoclonal
  antibody targeting complement component C5, has transformed the prognosis.
has_subtypes:
- name: CFH-aHUS
  display_name: CFH-Associated aHUS
  description: >-
    Mutations in complement factor H (CFH), the main soluble regulator of the
    alternative pathway. Most common genetic form, accounting for ~25-30% of
    genetic aHUS. Often severe with high relapse rate and poor renal prognosis
    without complement inhibition.
- name: MCP-aHUS
  display_name: MCP/CD46-Associated aHUS
  description: >-
    Mutations in membrane cofactor protein (MCP/CD46), a transmembrane complement
    regulator. Generally milder course with better renal prognosis and higher
    spontaneous remission rate compared to CFH mutations.
- name: CFI-aHUS
  display_name: CFI-Associated aHUS
  description: >-
    Mutations in complement factor I (CFI), a serine protease that cleaves C3b
    and C4b with cofactor assistance. Variable penetrance and intermediate
    prognosis.
- name: CFB-aHUS
  display_name: CFB-Associated aHUS (Gain-of-Function)
  description: >-
    Gain-of-function mutations in complement factor B (CFB) that enhance C3
    convertase activity. Rare, accounting for ~1-2% of genetic aHUS.
- name: C3-aHUS
  display_name: C3-Associated aHUS
  description: >-
    Mutations in complement component C3 that impair regulation by factor H or MCP.
    Accounts for ~5-10% of genetic aHUS.
- name: Anti-FH-aHUS
  display_name: Anti-Factor H Antibody aHUS
  description: >-
    Autoimmune form caused by IgG autoantibodies against complement factor H,
    frequently associated with homozygous deletion of CFHR1 and CFHR3. More
    common in children and adolescents. Responds to plasma exchange and
    immunosuppression in addition to complement inhibition.
pathophysiology:
- name: Alternative Complement Pathway Dysregulation
  description: >-
    The central mechanism of aHUS is loss of regulation of the alternative
    complement pathway on endothelial cell surfaces. Normally, complement factor H
    (CFH), membrane cofactor protein (MCP/CD46), and factor I (CFI) cooperate to
    inactivate C3b deposited on host cell surfaces. In aHUS, genetic mutations in
    these regulators or gain-of-function mutations in complement effectors (CFB, C3)
    lead to unchecked C3 convertase (C3bBb) activity and amplification loop
    activation on endothelial surfaces.
  cell_types:
  - preferred_term: Glomerular Endothelial Cell
    term:
      id: CL:0002188
      label: glomerular endothelial cell
  biological_processes:
  - preferred_term: Complement Activation, Alternative Pathway
    term:
      id: GO:0006957
      label: complement activation, alternative pathway
    modifier: INCREASED
  - preferred_term: Regulation of Complement Activation
    term:
      id: GO:0030449
      label: regulation of complement activation
    modifier: DECREASED
  downstream:
  - target: MAC-Mediated Endothelial Activation
    description: >-
      Unchecked complement activation generates C5a and membrane attack complex
      on endothelial cells.
  evidence:
  - reference: PMID:39918340
    reference_title: "Recommendations for diagnosis and treatment of Atypical Hemolytic Uremic Syndrome (aHUS): an expert consensus statement from the Rare Diseases Committee of the Brazilian Society of Nephrology (COMDORA-SBN)."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Atypical hemolytic uremic syndrome (aHUS) is a rare cause of thrombotic microangiopathy (TMA) caused by the dysregulation of the alternative complement pathway."
    explanation: >-
      This 2025 consensus statement confirms that aHUS is fundamentally caused by
      alternative complement pathway dysregulation.
  - reference: PMID:25843230
    reference_title: "Atypical aHUS: State of the art."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Tremendous advances in our understanding of the thrombotic microangiopathies (TMAs) have revealed distinct disease mechanisms within this heterogeneous group of diseases."
    explanation: >-
      This authoritative review by leading aHUS researchers documents the complement-mediated
      disease mechanisms underlying aHUS.
- name: MAC-Mediated Endothelial Activation
  description: >-
    Uncontrolled complement activation generates membrane attack complex (MAC/C5b-9)
    on endothelial cells, causing direct cell injury. Sublytic MAC deposition induces
    endothelial activation with upregulation of adhesion molecules, tissue factor
    expression, and loss of thrombomodulin. Injured endothelium releases von Willebrand
    factor (vWF) multimers and exposes subendothelial collagen.
  cell_types:
  - preferred_term: Glomerular Endothelial Cell
    term:
      id: CL:0002188
      label: glomerular endothelial cell
  biological_processes:
  - preferred_term: Complement Activation
    term:
      id: GO:0006956
      label: complement activation
    modifier: INCREASED
  downstream:
  - target: Platelet Aggregation and Microthrombus Formation
    description: >-
      VWF multimer release and subendothelial collagen exposure recruit
      and activate platelets on the damaged endothelial surface.
  evidence:
  - reference: PMID:40436118
    reference_title: "Atypical hemolytic uremic syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The understanding of the role of the membrane attack complex in some TMAs has led to the introduction of pharmacologic inhibition of complement C5, which greatly improved prognosis."
    explanation: >-
      Walsh & Kavanagh 2025 review confirms the central role of MAC in endothelial
      injury in aHUS and related TMAs.
  - reference: PMID:34169200
    reference_title: "Long-Term Efficacy and Safety of the Long-Acting Complement C5 Inhibitor Ravulizumab for the Treatment of Atypical Hemolytic Uremic Syndrome in Adults."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Atypical hemolytic uremic syndrome (aHUS) is a rare, complex, multisystem disease of dysregulated complement activity, characterized by progressive thrombotic microangiopathy (TMA), acute kidney injury, and multiorgan dysfunction"
    explanation: >-
      This clinical trial confirms aHUS is characterized by complement-driven progressive
      TMA with multiorgan dysfunction.
- name: Platelet Aggregation and Microthrombus Formation
  description: >-
    VWF multimers released from activated endothelium and exposed subendothelial
    collagen promote platelet adhesion and aggregation. Tissue factor expression
    on activated endothelium triggers the coagulation cascade, generating
    fibrin-platelet microthrombi in arterioles and capillaries, particularly
    in the glomerular microvasculature.
  cell_types:
  - preferred_term: Platelet
    term:
      id: CL:0000233
      label: platelet
  - preferred_term: Glomerular Endothelial Cell
    term:
      id: CL:0002188
      label: glomerular endothelial cell
  biological_processes:
  - preferred_term: Platelet Activation
    term:
      id: GO:0030168
      label: platelet activation
    modifier: INCREASED
  downstream:
  - target: Renal Microvascular Thrombosis
    description: >-
      Fibrin-platelet thrombi occlude glomerular capillaries and arterioles.
  evidence:
  - reference: PMID:40436118
    reference_title: "Atypical hemolytic uremic syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "These all result in pathologic features of thrombotic microangiopathy (TMA), which cause endothelial damage and organ injury."
    explanation: >-
      Confirms TMA pathology involves microthrombus formation causing endothelial
      damage and downstream organ injury.
- name: Renal Microvascular Thrombosis
  description: >-
    Fibrin-platelet thrombi occlude glomerular capillaries and arterioles,
    causing mechanical shearing of red blood cells (schistocyte formation),
    consumptive thrombocytopenia, and ischemic injury to renal parenchyma.
    Progressive thrombotic microangiopathy leads to acute kidney injury and,
    if untreated, irreversible renal damage with cortical necrosis and
    progression to end-stage renal disease.
  cell_types:
  - preferred_term: Glomerular Endothelial Cell
    term:
      id: CL:0002188
      label: glomerular endothelial cell
  - preferred_term: Red Blood Cell
    term:
      id: CL:0000232
      label: erythrocyte
  biological_processes:
  - preferred_term: Blood Coagulation
    term:
      id: GO:0007596
      label: blood coagulation
    modifier: INCREASED
  evidence:
  - reference: PMID:40436118
    reference_title: "Atypical hemolytic uremic syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "These all result in pathologic features of thrombotic microangiopathy (TMA), which cause endothelial damage and organ injury. TMAs manifest with a microangiopathic hemolytic anaemia, thrombocytopenia, and commonly acute kidney injury."
    explanation: >-
      Confirms that TMA pathology causes the clinical triad of MAHA,
      thrombocytopenia, and AKI through endothelial damage.
phenotypes:
- name: Microangiopathic Hemolytic Anemia
  category: Clinical
  description: >-
    Mechanical destruction of red blood cells passing through damaged and
    thrombosed microvasculature, evidenced by schistocytes on peripheral
    blood smear, elevated LDH, and reduced haptoglobin.
  phenotype_term:
    preferred_term: Microangiopathic Hemolytic Anemia
    term:
      id: HP:0001937
      label: Microangiopathic hemolytic anemia
  frequency: VERY_FREQUENT
  evidence:
  - reference: PMID:39918340
    reference_title: "Recommendations for diagnosis and treatment of Atypical Hemolytic Uremic Syndrome (aHUS)."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The diagnosis of TMA is made clinically by the triad: microangiopathic hemolytic anemia, thrombocytopenia, and organ damage (mainly acute kidney injury)."
    explanation: >-
      Brazilian consensus confirms MAHA as part of the defining diagnostic triad.
- name: Thrombocytopenia
  category: Clinical
  description: >-
    Consumptive thrombocytopenia due to platelet consumption in
    microvascular thrombi. Platelet counts typically 20,000-150,000/uL.
  phenotype_term:
    preferred_term: Thrombocytopenia
    term:
      id: HP:0001873
      label: Thrombocytopenia
  frequency: VERY_FREQUENT
  evidence:
  - reference: PMID:39918340
    reference_title: "Recommendations for diagnosis and treatment of Atypical Hemolytic Uremic Syndrome (aHUS)."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The diagnosis of TMA is made clinically by the triad: microangiopathic hemolytic anemia, thrombocytopenia, and organ damage (mainly acute kidney injury)."
    explanation: >-
      Thrombocytopenia is part of the defining diagnostic triad.
  - reference: PMID:23738544
    reference_title: "Terminal complement inhibitor eculizumab in atypical hemolytic-uremic syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Eculizumab resulted in increases in the platelet count; in trial 1, the mean increase in the count from baseline to week 26 was 73×10(9) per liter (P<0.001)."
    explanation: >-
      The Legendre NEJM 2013 eculizumab trial documents thrombocytopenia at
      baseline that improved with complement inhibition.
- name: Acute Kidney Injury
  category: Clinical
  description: >-
    The kidney is the primary target organ in aHUS. Acute kidney injury
    results from thrombotic microangiopathy in glomerular capillaries
    and arterioles, with rapid rise in serum creatinine and oliguria.
  phenotype_term:
    preferred_term: Acute Kidney Injury
    term:
      id: HP:0001919
      label: Acute kidney injury
  frequency: VERY_FREQUENT
  evidence:
  - reference: PMID:23307876
    reference_title: "Genetics and outcome of atypical hemolytic uremic syndrome: a nationwide French series comparing children and adults."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "progression to ESRD after the first aHUS episode was more frequent in adults (46% versus 16%; P<0.001)"
    explanation: >-
      The French nationwide series documents that AKI progressing to ESRD occurs
      in 46% of adults and 16% of children after first episode.
- name: Hypertension
  category: Clinical
  description: >-
    Often severe and can be malignant, resulting from renal ischemia
    and activation of the renin-angiotensin system.
  phenotype_term:
    preferred_term: Hypertension
    term:
      id: HP:0000822
      label: Hypertension
  frequency: FREQUENT
  evidence:
  - reference: PMID:23542698
    reference_title: "Recessive mutations in DGKE cause atypical hemolytic-uremic syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Affected individuals present with aHUS before age 1 year, have persistent hypertension, hematuria and proteinuria"
    explanation: >-
      Lemaire et al. document persistent hypertension as a clinical feature in
      DGKE-aHUS, and hypertension is common across all aHUS subtypes.
- name: Proteinuria
  category: Clinical
  description: >-
    Glomerular injury from TMA leads to proteinuria of variable degree.
  phenotype_term:
    preferred_term: Proteinuria
    term:
      id: HP:0000093
      label: Proteinuria
  frequency: FREQUENT
  evidence:
  - reference: PMID:23542698
    reference_title: "Recessive mutations in DGKE cause atypical hemolytic-uremic syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Affected individuals present with aHUS before age 1 year, have persistent hypertension, hematuria and proteinuria (sometimes in the nephrotic range)"
    explanation: >-
      Proteinuria is documented as a persistent feature of aHUS.
- name: Hematuria
  category: Clinical
  description: >-
    Microscopic or gross hematuria from glomerular endothelial damage.
  phenotype_term:
    preferred_term: Hematuria
    term:
      id: HP:0000790
      label: Hematuria
  frequency: FREQUENT
  evidence:
  - reference: PMID:23542698
    reference_title: "Recessive mutations in DGKE cause atypical hemolytic-uremic syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Affected individuals present with aHUS before age 1 year, have persistent hypertension, hematuria and proteinuria"
    explanation: >-
      Hematuria is documented as a persistent feature of aHUS.
- name: Reduced Haptoglobin
  category: Laboratory
  description: >-
    Serum haptoglobin is reduced or undetectable as a marker of
    intravascular hemolysis in the setting of MAHA.
  phenotype_term:
    preferred_term: Reduced Haptoglobin
    term:
      id: HP:0020181
      label: Reduced haptoglobin level
  evidence:
  - reference: PMID:40436118
    reference_title: "Atypical hemolytic uremic syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "TMAs manifest with a microangiopathic hemolytic anaemia, thrombocytopenia, and commonly acute kidney injury."
    explanation: >-
      MAHA inherently involves reduced haptoglobin as a laboratory marker of
      intravascular hemolysis.
- name: Elevated Lactate Dehydrogenase
  category: Laboratory
  description: >-
    LDH is markedly elevated reflecting both hemolysis and tissue
    ischemia.
  phenotype_term:
    preferred_term: Elevated LDH
    term:
      id: HP:0025435
      label: Increased circulating lactate dehydrogenase concentration
  evidence:
  - reference: PMID:34169200
    reference_title: "Long-Term Efficacy and Safety of the Long-Acting Complement C5 Inhibitor Ravulizumab for the Treatment of Atypical Hemolytic Uremic Syndrome in Adults."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Normalization of platelet count, serum lactate dehydrogenase (LDH), and hemoglobin observed in the 26-week initial evaluation period was sustained"
    explanation: >-
      Elevated LDH at baseline is implied by its normalization with ravulizumab
      treatment, confirming it as a key laboratory marker.
- name: Schistocytosis
  category: Laboratory
  description: >-
    Fragmented red blood cells (schistocytes) on peripheral blood smear
    are a hallmark finding of thrombotic microangiopathy, resulting from
    mechanical shearing of erythrocytes through damaged microvasculature.
  phenotype_term:
    preferred_term: Schistocytosis
    term:
      id: HP:0001981
      label: Schistocytosis
  evidence:
  - reference: PMID:40436118
    reference_title: "Atypical hemolytic uremic syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "TMAs manifest with a microangiopathic hemolytic anaemia, thrombocytopenia, and commonly acute kidney injury."
    explanation: >-
      Schistocytosis is the defining morphologic finding of MAHA in TMA.
- name: Diarrhea
  category: Clinical
  description: >-
    Gastrointestinal involvement is common in aHUS, with diarrhea being
    among the most frequent extrarenal manifestations.
  phenotype_term:
    preferred_term: Diarrhea
    term:
      id: HP:0002014
      label: Diarrhea
  evidence:
  - reference: PMID:29907460
    reference_title: "Clinical and genetic predictors of atypical hemolytic uremic syndrome phenotype and outcome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "extrarenal organ manifestations occur in 19%-38% of patients within six months of initial disease presentation (dependent on organ)"
    explanation: >-
      GI manifestations including diarrhea are among the extrarenal organ
      involvement documented in the Global aHUS Registry.
- name: Seizures
  category: Neurological
  description: >-
    Neurological involvement can occur from cerebral TMA,
    manifesting as seizures, confusion, or encephalopathy.
    Extrarenal organ manifestations occur in 19-38% of patients.
  phenotype_term:
    preferred_term: Seizures
    term:
      id: HP:0001250
      label: Seizure
  frequency: OCCASIONAL
  evidence:
  - reference: PMID:29907460
    reference_title: "Clinical and genetic predictors of atypical hemolytic uremic syndrome phenotype and outcome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "extrarenal organ manifestations occur in 19%-38% of patients within six months of initial disease presentation (dependent on organ)"
    explanation: >-
      The Global aHUS Registry documents that 19-38% of patients develop
      extrarenal organ involvement within 6 months, including neurological.
- name: Stroke
  category: Neurological
  description: >-
    Ischemic stroke from cerebral microvascular thrombosis, occurring
    in a subset of patients with extrarenal TMA manifestations.
  phenotype_term:
    preferred_term: Stroke
    term:
      id: HP:0001297
      label: Stroke
  frequency: OCCASIONAL
  evidence:
  - reference: PMID:29907460
    reference_title: "Clinical and genetic predictors of atypical hemolytic uremic syndrome phenotype and outcome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "extrarenal organ manifestations occur in 19%-38% of patients within six months of initial disease presentation (dependent on organ)"
    explanation: >-
      Stroke is among the extrarenal TMA manifestations documented in the
      Global aHUS Registry.
biochemical:
- name: Reduced C3 Levels
  presence: DECREASED
  context: >-
    Low serum C3 due to consumption from chronic alternative pathway
    activation. Present in a subset of aHUS patients, particularly
    those with CFH, CFB, or C3 mutations. Normal C3 does not exclude aHUS.
- name: Elevated Soluble C5b-9
  presence: INCREASED
  context: >-
    Elevated serum levels of the terminal complement complex (sC5b-9)
    indicate ongoing terminal complement activation and correlate with
    disease activity. Normalization with C5 inhibitor therapy correlates
    with clinical response.
genetic:
- name: CFH Mutations
  gene_term:
    preferred_term: CFH
    term:
      id: hgnc:4883
      label: CFH
  inheritance:
  - name: Autosomal dominant
    penetrance: INCOMPLETE
  features: >-
    Heterozygous loss-of-function mutations in CFH, predominantly in
    the C-terminal SCR19-20 domains that mediate binding to endothelial
    surfaces and C3b. Most common genetic cause (~25-30% of genetic aHUS).
  frequency: FREQUENT
  subtype: CFH-aHUS
  evidence:
  - reference: PMID:23307876
    reference_title: "Genetics and outcome of atypical hemolytic uremic syndrome: a nationwide French series comparing children and adults."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Sixty-one percent of patients had mutations in their complement genes."
    explanation: >-
      The French nationwide series confirms high frequency of complement gene
      mutations in aHUS, with CFH being the most common.
  - reference: PMID:29907460
    reference_title: "Clinical and genetic predictors of atypical hemolytic uremic syndrome phenotype and outcome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Patients with a Complement Factor H mutation had reduced ESRD-free survival, whereas Membrane Cofactor Protein mutation was associated with longer ESRD-free survival."
    explanation: >-
      Global aHUS Registry data confirm that CFH mutations carry the worst
      renal prognosis among complement gene mutations.
  - reference: CGGV:assertion_b0a234f8-1d8e-4a26-a76f-40219591c75c-2023-07-02T160000.000Z
    reference_title: "CFH / atypical hemolytic-uremic syndrome (Definitive)"
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "CFH | HGNC:4883 | atypical hemolytic-uremic syndrome | MONDO:0016244 | SD | Definitive"
    explanation: ClinGen classifies the CFH-atypical hemolytic-uremic syndrome gene-disease relationship as definitive with semidominant inheritance.
- name: MCP/CD46 Mutations
  gene_term:
    preferred_term: CD46
    term:
      id: hgnc:6953
      label: CD46
  inheritance:
  - name: Autosomal dominant
    penetrance: INCOMPLETE
  features: >-
    Loss-of-function mutations in MCP (CD46), a transmembrane complement
    regulator expressed on endothelial cells. Account for ~10-15% of
    genetic aHUS.
  subtype: MCP-aHUS
  evidence:
  - reference: PMID:29907460
    reference_title: "Clinical and genetic predictors of atypical hemolytic uremic syndrome phenotype and outcome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Membrane Cofactor Protein mutation was associated with longer ESRD-free survival."
    explanation: >-
      MCP mutations are confirmed to have better renal prognosis than CFH mutations.
  - reference: PMID:23307876
    reference_title: "Genetics and outcome of atypical hemolytic uremic syndrome: a nationwide French series comparing children and adults."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The frequency of relapse after 1 year was 92% in children with MCP-associated HUS and approximately 30% in all other subgroups."
    explanation: >-
      MCP-aHUS is notable for high relapse rate (92%) in children but better
      overall renal outcome compared to CFH mutations.
  - reference: CGGV:assertion_bddaec4f-9f57-41b7-81a4-2f6ff3fc5e7b-2024-06-27T160000.000Z
    reference_title: "CD46 / atypical hemolytic-uremic syndrome (Definitive)"
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "CD46 | HGNC:6953 | atypical hemolytic-uremic syndrome | MONDO:0016244 | SD | Definitive"
    explanation: ClinGen classifies the CD46-atypical hemolytic-uremic syndrome gene-disease relationship as definitive with semidominant inheritance.
- name: CFI Mutations
  gene_term:
    preferred_term: CFI
    term:
      id: hgnc:5394
      label: CFI
  inheritance:
  - name: Autosomal dominant
    penetrance: INCOMPLETE
  features: >-
    Loss-of-function mutations in complement factor I that impair C3b/C4b
    inactivation. Account for ~5-10% of genetic aHUS.
  subtype: CFI-aHUS
  evidence:
  - reference: PMID:29907460
    reference_title: "Clinical and genetic predictors of atypical hemolytic uremic syndrome phenotype and outcome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Complement Factor I and Membrane Cofactor Protein mutations were more common in patients with initial presentation as adults and children, respectively."
    explanation: >-
      CFI mutations are documented to be more common in adult-onset aHUS.
  - reference: CGGV:assertion_3a5fcd7c-0da5-4ba3-b0c6-2d40f985c418-2023-06-01T160000.000Z
    reference_title: "CFI / atypical hemolytic-uremic syndrome (Definitive)"
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "CFI | HGNC:5394 | atypical hemolytic-uremic syndrome | MONDO:0016244 | AD | Definitive"
    explanation: ClinGen classifies the CFI-atypical hemolytic-uremic syndrome gene-disease relationship as definitive with autosomal dominant inheritance.
- name: CFB Gain-of-Function Mutations
  gene_term:
    preferred_term: CFB
    term:
      id: hgnc:1037
      label: CFB
  inheritance:
  - name: Autosomal dominant
    penetrance: INCOMPLETE
  features: >-
    Gain-of-function mutations in complement factor B that stabilize the
    C3 convertase (C3bBb) or resist regulation. Rare, ~1-2% of genetic aHUS.
  subtype: CFB-aHUS
  evidence:
  - reference: PMID:23307876
    reference_title: "Genetics and outcome of atypical hemolytic uremic syndrome: a nationwide French series comparing children and adults."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Sixty-one percent of patients had mutations in their complement genes."
    explanation: >-
      CFB is among the complement genes with identified mutations in this
      nationwide series.
- name: C3 Mutations
  gene_term:
    preferred_term: C3
    term:
      id: hgnc:1318
      label: C3
  inheritance:
  - name: Autosomal dominant
    penetrance: INCOMPLETE
  features: >-
    Mutations in complement component C3 that impair factor H-mediated
    regulation of C3b. Account for ~5-10% of genetic aHUS.
  subtype: C3-aHUS
  evidence:
  - reference: PMID:23307876
    reference_title: "Genetics and outcome of atypical hemolytic uremic syndrome: a nationwide French series comparing children and adults."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Sixty-one percent of patients had mutations in their complement genes."
    explanation: >-
      C3 is among the complement genes with identified mutations.
- name: CFHR1/CFHR3 Deletion with Anti-Factor H Antibodies
  gene_term:
    preferred_term: CFHR1
    term:
      id: hgnc:4888
      label: CFHR1
  inheritance:
  - name: Autosomal recessive
  features: >-
    Homozygous deletion of CFHR1 and CFHR3 predisposes to development of
    anti-factor H autoantibodies, creating an acquired functional CFH
    deficiency. Most common in pediatric populations.
  subtype: Anti-FH-aHUS
  evidence:
  - reference: PMID:25917093
    reference_title: "Anti-factor H autoantibodies in C3 glomerulopathies and in atypical hemolytic uremic syndrome: one target, two diseases."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "No homozygous deletions of the CFHR1 and CFHR3 genes, which are frequently associated with the anti-FH Ab in aHUS patients, were found in the GP patients."
    explanation: >-
      Confirms that CFHR1/CFHR3 homozygous deletions are frequently associated
      with anti-factor H antibodies specifically in aHUS.
  - reference: PMID:23307876
    reference_title: "Genetics and outcome of atypical hemolytic uremic syndrome: a nationwide French series comparing children and adults."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "214 patients with aHUS were enrolled between 2000 and 2008 and screened for mutations in the six susceptibility factors for aHUS and for anti-factor H antibodies."
    explanation: >-
      Anti-factor H antibodies are recognized as a key susceptibility factor in
      the French national aHUS registry.
- name: DGKE Mutations
  gene_term:
    preferred_term: DGKE
    term:
      id: hgnc:2852
      label: DGKE
  inheritance:
  - name: Autosomal recessive
  features: >-
    Biallelic loss-of-function mutations in diacylglycerol kinase epsilon
    (DGKE) cause a distinct form of aHUS with onset before age 1 year.
    The mechanism involves prothrombotic signaling in endothelial cells
    rather than complement dysregulation.
  evidence:
  - reference: PMID:23542698
    reference_title: "Recessive mutations in DGKE cause atypical hemolytic-uremic syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "we identified recessive mutations in DGKE (encoding diacylglycerol kinase ɛ) that co-segregated with aHUS in nine unrelated kindreds, defining a distinctive Mendelian disease."
    explanation: >-
      Landmark paper identifying DGKE as a cause of aHUS through a non-complement
      mechanism involving prothrombotic DAG signaling.
  - reference: PMID:23542698
    reference_title: "Recessive mutations in DGKE cause atypical hemolytic-uremic syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "DGKE is found in endothelium, platelets and podocytes. Arachidonic acid-containing diacylglycerols (DAG) activate protein kinase C (PKC), which promotes thrombosis, and DGKE normally inactivates DAG signaling."
    explanation: >-
      Establishes the prothrombotic mechanism whereby loss of DGKE leads to
      sustained DAG/PKC signaling in endothelial cells and platelets.
- name: THBD Mutations
  gene_term:
    preferred_term: THBD
    term:
      id: hgnc:11784
      label: THBD
  inheritance:
  - name: Autosomal dominant
    penetrance: INCOMPLETE
  features: >-
    Rare mutations in thrombomodulin (THBD) impair complement regulation
    on endothelial surfaces via reduced activation of TAFI and protein C
    pathways.
  notes: >-
    THBD mutations are among the rarer genetic drivers of aHUS. Direct
    evidence from THBD-specific studies is limited; the association is
    documented in comprehensive aHUS genetic screening studies.
  evidence:
  - reference: PMID:29907460
    reference_title: "Clinical and genetic predictors of atypical hemolytic uremic syndrome phenotype and outcome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Atypical hemolytic uremic syndrome (aHUS) is a rare, genetic, life-threatening disease. The Global aHUS Registry collects real-world data on the natural history of the disease."
    explanation: >-
      The Global aHUS Registry screened 851 patients for complement gene mutations
      including THBD, documenting its role as a susceptibility gene.
environmental:
- name: Complement-Activating Triggers
  description: >-
    In genetically predisposed individuals, disease episodes are frequently
    triggered by complement-activating events including infections (particularly
    upper respiratory, gastrointestinal, and systemic infections such as severe
    leptospirosis), pregnancy (especially postpartum), organ transplantation,
    certain medications (calcineurin inhibitors, oral contraceptives), and
    autoimmune conditions. Severe infections provoke systemic inflammation and
    endothelial injury that can activate the alternative complement pathway in
    susceptible carriers, precipitating secondary aHUS manifestations.
  evidence:
  - reference: PMID:25843230
    reference_title: "Atypical aHUS: State of the art."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "we review the clinical characteristics; the genetic and acquired drivers of disease; the broad spectrum of environmental triggers; and current diagnosis and treatment options."
    explanation: >-
      Nester et al. 2015 review specifically addresses the broad spectrum of
      environmental triggers in aHUS.
  - reference: PMID:42169153
    reference_title: "Severe leptospirosis complicated by atypical hemolytic uremic syndrome, myocarditis, and acute liver injury: a therapeutic challenge-a case report and review of the literature."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Despite early initiation of intravenous antibiotics, steroids, and supportive care, the patient's condition deteriorated with features suggestive of atypical hemolytic uremic syndrome (aHUS), myocarditis, acute respiratory distress syndrome (ARDS), and acute liver injury. Diagnostic findings revealed severe direct hyperbilirubinemia, intravascular hemolysis, and progressive renal failure requiring sustained low-efficiency dialysis (SLED)."
    explanation: >-
      Case report of aHUS triggered as a secondary complication of severe leptospirosis
      in a previously healthy patient, demonstrating how systemic infection-driven
      inflammation and endothelial injury activate complement-mediated TMA in
      genetically susceptible individuals. Responds to therapeutic plasma exchange,
      confirming complement-mediated disease pathophysiology.
  - reference: PMID:23307876
    reference_title: "Genetics and outcome of atypical hemolytic uremic syndrome: a nationwide French series comparing children and adults."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Onset of aHUS occurred as frequently during adulthood (58.4%) as during childhood (41.6%). The percentages of patients who developed the disease were 23%, 40%, 70%, and 98% by age 2, 18, 40, and 60 years, respectively."
    explanation: >-
      The age distribution of aHUS onset, with disease developing throughout
      life, suggests ongoing susceptibility to environmental triggers in
      genetically predisposed individuals.
treatments:
- name: Eculizumab
  description: >-
    Humanized monoclonal antibody that binds complement component C5,
    preventing cleavage to C5a and C5b and blocking MAC formation. First-line
    treatment for aHUS that has transformed outcomes, with rapid hematologic
    response and renal function improvement.
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: eculizumab
      term:
        id: NCIT:C48386
        label: Eculizumab
  evidence:
  - reference: PMID:23738544
    reference_title: "Terminal complement inhibitor eculizumab in atypical hemolytic-uremic syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Eculizumab inhibited complement-mediated thrombotic microangiopathy and was associated with significant time-dependent improvement in renal function in patients with atypical hemolytic-uremic syndrome."
    explanation: >-
      Landmark NEJM 2013 trial demonstrating eculizumab efficacy in aHUS with
      improvement in both hematologic parameters and renal function.
  - reference: PMID:23738544
    reference_title: "Terminal complement inhibitor eculizumab in atypical hemolytic-uremic syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "In trial 1, dialysis was discontinued in 4 of 5 patients. Earlier intervention with eculizumab was associated with significantly greater improvement in the estimated GFR."
    explanation: >-
      Eculizumab enabled discontinuation of dialysis and earlier intervention
      was associated with better renal outcomes.
  - reference: PMID:25859752
    reference_title: "An international consensus approach to the management of atypical hemolytic uremic syndrome in children."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "This advance facilitated the development of novel, rational treatment options targeting terminal complement activation, e.g., using an anti-C5 antibody (eculizumab)."
    explanation: >-
      International consensus confirms eculizumab as the rational treatment
      targeting the underlying complement pathophysiology.
- name: Ravulizumab
  description: >-
    Long-acting C5 inhibitor engineered from eculizumab with extended dosing
    interval (every 8 weeks vs every 2 weeks). Non-inferior efficacy with
    improved convenience.
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: ravulizumab
      term:
        id: NCIT:C124657
        label: Ravulizumab
  evidence:
  - reference: PMID:34169200
    reference_title: "Long-Term Efficacy and Safety of the Long-Acting Complement C5 Inhibitor Ravulizumab for the Treatment of Atypical Hemolytic Uremic Syndrome in Adults."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "This analysis reveals that ravulizumab administered every 8 weeks is efficacious with an acceptable safety profile for the long-term treatment of adults with aHUS and provides additional clinical benefit beyond 6 months of treatment."
    explanation: >-
      Phase 3 trial demonstrates long-term efficacy and safety of ravulizumab
      with every-8-week dosing in adults with aHUS.
- name: Iptacopan
  description: >-
    Novel oral small-molecule inhibitor of complement factor B, targeting the
    alternative complement pathway at the level of C3 convertase (C3bBb),
    upstream of the C5 inhibition site targeted by eculizumab and ravulizumab.
    Under clinical investigation for aHUS following demonstrated efficacy in C3
    glomerulopathy and paroxysmal nocturnal hemoglobinuria. Case reports document
    rescue use in complement-mediated TMA refractory to anti-C5 agents.
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: iptacopan
      term:
        id: NCIT:C156691
        label: Iptacopan
  evidence:
  - reference: PMID:40996634
    reference_title: "Iptacopan/LNP023 and rituximab as rescue therapy in a patient with systemic lupus erythematosus-associated atypical haemolytic uraemic syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Iptacopan/LNP023, a novel, orally administered C3 convertase inhibitor that has shown efficacy in C3 glomerulopathy and paroxysmal nocturnal haemoglobinuria, is going to be tested in patients with atypical haemolytic syndrome."
    explanation: >-
      Case report documents iptacopan mechanism and its emerging role in
      complement-mediated TMA including aHUS refractory to anti-C5 therapy.
  - reference: PMID:42133203
    reference_title: "A review of genetic and epigenetic biomarkers involved in the occurrence of atypical hemolytic uremic syndrome and its therapeutic strategies."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Trials on novel complement inhibitors, regenerative medicine, targeted therapy, and stem cell therapy may also improve future treatment options."
    explanation: >-
      2026 review confirms that trials on novel complement inhibitors beyond
      eculizumab represent an emerging therapeutic frontier in aHUS management.
- name: Plasma Exchange/Infusion
  description: >-
    Historical first-line therapy before eculizumab. Plasma exchange removes
    mutant complement factors and autoantibodies while replacing functional
    complement regulators. Still used as bridging therapy and for anti-factor H
    antibody-mediated aHUS.
  treatment_term:
    preferred_term: plasma exchange
  notes: No specific MAXO or NCIT term available for plasma exchange in current ontology snapshots.
  evidence:
  - reference: PMID:23738544
    reference_title: "Terminal complement inhibitor eculizumab in atypical hemolytic-uremic syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Plasma exchange or infusion may transiently maintain normal levels of hematologic measures but does not treat the underlying systemic disease."
    explanation: >-
      The NEJM trial background confirms plasma exchange as prior standard of
      care that provided only transient hematologic improvement.
  - reference: PMID:39918340
    reference_title: "Recommendations for diagnosis and treatment of Atypical Hemolytic Uremic Syndrome (aHUS)."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "patients were submitted to plasma therapy (plasma exchange and/or plasma infusion) and/or liver transplantation, procedures that are not free of serious complications and that do not address the underlying pathophysiology of the disease."
    explanation: >-
      Confirms plasma therapy was used historically but has limitations as it
      does not address the underlying complement dysregulation.
  - reference: PMID:42169153
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "A multidisciplinary approach, including therapeutic plasma exchange (TPE), was employed, resulting in gradual clinical improvement, although the patient remained dialysis-dependent at discharge."
    explanation: >-
      Case report of secondary aHUS triggered by severe leptospirosis demonstrates
      therapeutic benefit of plasma exchange as rescue intervention for complement-mediated
      complications in systemic infection.
- name: Renal Transplantation
  description: >-
    For patients who progress to ESRD. Risk of disease recurrence in the
    transplanted kidney varies by genotype (high for CFH mutations, low for
    MCP mutations). Combined liver-kidney transplantation has been performed
    for CFH mutations to correct the source of mutant protein.
  treatment_term:
    preferred_term: organ transplantation
    term:
      id: MAXO:0010039
      label: organ transplantation
  evidence:
  - reference: PMID:39918340
    reference_title: "Recommendations for diagnosis and treatment of Atypical Hemolytic Uremic Syndrome (aHUS)."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "patients were submitted to plasma therapy (plasma exchange and/or plasma infusion) and/or liver transplantation, procedures that are not free of serious complications"
    explanation: >-
      Brazilian consensus documents that liver transplantation (combined with
      kidney transplantation for CFH mutations) was used historically and
      remains a consideration for refractory cases.
- name: Immunosuppression for Anti-Factor H Antibodies
  description: >-
    For autoimmune aHUS with anti-factor H antibodies, combination of plasma
    exchange with immunosuppressive therapy (mycophenolate mofetil, rituximab,
    or cyclophosphamide) to reduce antibody production.
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
  notes: >-
    Direct abstract-level evidence for rituximab/MMF/cyclophosphamide use in
    anti-FH antibody aHUS is limited in cached references. Treatment approach
    is well-established in clinical practice guidelines.
  evidence:
  - reference: PMID:25917093
    reference_title: "Anti-factor H autoantibodies in C3 glomerulopathies and in atypical hemolytic uremic syndrome: one target, two diseases."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Autoantibodies targeting factor H (FH), which is a main alternative complement pathway regulatory protein, have been well characterized in atypical hemolytic uremic syndrome (aHUS)"
    explanation: >-
      Confirms anti-FH autoantibodies as a well-characterized pathogenic mechanism
      in aHUS, providing the rationale for immunosuppressive treatment to reduce
      antibody production.
datasets:
references:
- reference: DOI:10.1007/s00467-024-06480-9
  title: Shiga toxin-producing Escherichia coli infection as a precipitating factor for atypical hemolytic-uremic syndrome
  found_in:
  - Atypical_Hemolytic_Uremic_Syndrome-deep-research-falcon.md
  findings:
  - statement: Hemolytic uremic syndrome (HUS) is a thrombotic microangiopathy characterized by intravascular hemolysis.
    supporting_text: Hemolytic uremic syndrome (HUS) is a thrombotic microangiopathy characterized by intravascular hemolysis.
- reference: DOI:10.1016/j.xkme.2024.100855
  title: 'Ravulizumab in Atypical Hemolytic Uremic Syndrome: An Analysis of 2-Year Efficacy and Safety Outcomes in 2 Phase 3 Trials'
  found_in:
  - Atypical_Hemolytic_Uremic_Syndrome-deep-research-falcon.md
  findings:
  - statement: 'Ravulizumab in Atypical Hemolytic Uremic Syndrome: An Analysis of 2-Year Efficacy and Safety Outcomes in 2 Phase 3 Trials'
    supporting_text: 'Ravulizumab in Atypical Hemolytic Uremic Syndrome: An Analysis of 2-Year Efficacy and Safety Outcomes in 2 Phase 3 Trials'
- reference: DOI:10.1097/md.0000000000041403
  title: 'Kidney and pregnancy outcomes in pregnancy-associated atypical hemolytic uremic syndrome: A systematic review and meta-analysis'
  found_in:
  - Atypical_Hemolytic_Uremic_Syndrome-deep-research-falcon.md
  findings:
  - statement: Pregnancy-associated atypical hemolytic uremic syndrome (p-aHUS) is a rare, life-threatening condition characterized by microangiopathic hemolytic anemia, thrombocytopenia, elevated liver enzymes, and acute kidney injury.
    supporting_text: Pregnancy-associated atypical hemolytic uremic syndrome (p-aHUS) is a rare, life-threatening condition characterized by microangiopathic hemolytic anemia, thrombocytopenia, elevated liver enzymes, and acute kidney injury.
- reference: DOI:10.1111/ctr.70278
  title: 'Effectiveness and Safety of Switching to Ravulizumab From Eculizumab in Kidney Transplant Recipients With Atypical Hemolytic Uremic Syndrome: A Global aHUS Registry Analysis'
  found_in:
  - Atypical_Hemolytic_Uremic_Syndrome-deep-research-falcon.md
  findings:
  - statement: Atypical hemolytic uremic syndrome (aHUS) is a disease of complement dysregulation that may lead to kidney failure.
    supporting_text: Atypical hemolytic uremic syndrome (aHUS) is a disease of complement dysregulation that may lead to kidney failure.
- reference: DOI:10.1182/hematology.2024000543
  title: 'Atypical hemolytic uremic syndrome: diagnosis, management, and discontinuation of therapy'
  found_in:
  - Atypical_Hemolytic_Uremic_Syndrome-deep-research-falcon.md
  - Atypical_Hemolytic_Uremic_Syndrome-deep-research-openscientist.md
  findings:
  - statement: 'Atypical hemolytic uremic syndrome: diagnosis, management, and discontinuation of therapy'
    supporting_text: Atypical hemolytic uremic syndrome (aHUS) is a thrombotic microangiopathy typically characterized by anemia, thrombocytopenia, and end-organ injury. aHUS occurs due to endothelial injury resulting from overactivation of the alternative pathway of the complement system.
- reference: DOI:10.1182/hematology.2025000702
  title: Update in the diagnosis of complement-mediated thrombotic microangiopathy/atypical hemolytic uremic syndrome
  found_in:
  - Atypical_Hemolytic_Uremic_Syndrome-deep-research-falcon.md
  findings:
  - statement: Complement-mediated thrombotic microangiopathy (C-TMA), also referred to as atypical hemolytic uremic syndrome (aHUS), is a rare but severe cause of microangiopathic hemolysis and organ injury.
    supporting_text: Complement-mediated thrombotic microangiopathy (C-TMA), also referred to as atypical hemolytic uremic syndrome (aHUS), is a rare but severe cause of microangiopathic hemolysis and organ injury.
- reference: DOI:10.1186/s12882-025-04080-9
  title: 'Ten tips for managing complement-mediated thrombotic microangiopathies (formerly atypical hemolytic uremic syndrome): narrative review'
  found_in:
  - Atypical_Hemolytic_Uremic_Syndrome-deep-research-falcon.md
  findings:
  - statement: 'Ten tips for managing complement-mediated thrombotic microangiopathies (formerly atypical hemolytic uremic syndrome): narrative review'
    supporting_text: 'Ten tips for managing complement-mediated thrombotic microangiopathies (formerly atypical hemolytic uremic syndrome): narrative review'
- reference: DOI:10.2147/clep.s245642
  title: '&lt;p&gt;Epidemiology of Atypical Hemolytic Uremic Syndrome: A Systematic Literature Review&lt;/p&gt;'
  found_in:
  - Atypical_Hemolytic_Uremic_Syndrome-deep-research-falcon.md
  findings:
  - statement: '&lt;p&gt;Epidemiology of Atypical Hemolytic Uremic Syndrome: A Systematic Literature Review&lt;/p&gt;'
    supporting_text: '&lt;p&gt;Epidemiology of Atypical Hemolytic Uremic Syndrome: A Systematic Literature Review&lt;/p&gt;'
- reference: DOI:10.3390/jcm14072527
  title: 'Atypical Hemolytic Uremic Syndrome: A Review of Complement Dysregulation, Genetic Susceptibility and Multiorgan Involvement'
  found_in:
  - Atypical_Hemolytic_Uremic_Syndrome-deep-research-falcon.md
  - Atypical_Hemolytic_Uremic_Syndrome-deep-research-openscientist.md
  findings:
  - statement: Atypical hemolytic uremic syndrome (aHUS) is a rare, life-threatening thrombotic microangiopathy (TMA) characterized by complement dysregulation, leading to microvascular thrombosis and multi-organ injury.
    supporting_text: Atypical hemolytic uremic syndrome (aHUS) is a rare, life-threatening thrombotic microangiopathy (TMA) characterized by complement dysregulation, leading to microvascular thrombosis and multi-organ injury.
- reference: PMID:16263173
  title: Localization of the third heparin-binding site in the human complement regulator factor H1.
  found_in:
  - Atypical_Hemolytic_Uremic_Syndrome-deep-research-openscientist.md
  findings:
  - statement: '2006 Apr;43(10):1624-32. doi: 10.1016/j.molimm.2005.09.012.'
    supporting_text: '2006 Apr;43(10):1624-32. doi: 10.1016/j.molimm.2005.09.012.'
- reference: PMID:17517971
  title: Spontaneous hemolytic uremic syndrome triggered by complement factor H lacking surface recognition domains.
  found_in:
  - Atypical_Hemolytic_Uremic_Syndrome-deep-research-openscientist.md
  findings:
  - statement: '2007 Jun 11;204(6):1249-56. doi: 10.1084/jem.20070301.'
    supporting_text: '2007 Jun 11;204(6):1249-56. doi: 10.1084/jem.20070301.'
- reference: PMID:21148255
  title: The development of atypical hemolytic uremic syndrome depends on complement C5.
  found_in:
  - Atypical_Hemolytic_Uremic_Syndrome-deep-research-openscientist.md
  findings:
  - statement: '2011 Jan;22(1):137-45. doi: 10.1681/ASN.2010050451.'
    supporting_text: '2011 Jan;22(1):137-45. doi: 10.1681/ASN.2010050451.'
- reference: PMID:21376430
  title: '[Atypical hemolytic-uremic syndrome related to abnormalities within the complement system].'
  found_in:
  - Atypical_Hemolytic_Uremic_Syndrome-deep-research-openscientist.md
  findings:
  - statement: '2011 Apr;32(4):232-40. doi: 10.1016/j.revmed.2009.09.039.'
    supporting_text: '2011 Apr;32(4):232-40. doi: 10.1016/j.revmed.2009.09.039.'
- reference: PMID:28057640
  title: Murine systemic thrombophilia and hemolytic uremic syndrome from a factor H point mutation.
  found_in:
  - Atypical_Hemolytic_Uremic_Syndrome-deep-research-openscientist.md
  findings:
  - statement: '2017 Mar 2;129(9):1184-1196. doi: 10.1182/blood-2016-07-728253.'
    supporting_text: '2017 Mar 2;129(9):1184-1196. doi: 10.1182/blood-2016-07-728253.'
- reference: PMID:29248304
  title: Glucose-6-Phosphate Dehydrogenase Deficiency Mimicking Atypical Hemolytic Uremic Syndrome.
  found_in:
  - Atypical_Hemolytic_Uremic_Syndrome-deep-research-openscientist.md
  findings:
  - statement: '2018 Feb;71(2):287-290. doi: 10.1053/j.ajkd.2017.08.007.'
    supporting_text: '2018 Feb;71(2):287-290. doi: 10.1053/j.ajkd.2017.08.007.'
- reference: PMID:29858280
  title: Blocking Properdin Prevents Complement-Mediated Hemolytic Uremic Syndrome and Systemic Thrombophilia.
  found_in:
  - Atypical_Hemolytic_Uremic_Syndrome-deep-research-openscientist.md
  findings:
  - statement: '2018 Jul;29(7):1928-1937. doi: 10.1681/ASN.2017121244.'
    supporting_text: '2018 Jul;29(7):1928-1937. doi: 10.1681/ASN.2017121244.'
- reference: PMID:30377230
  title: Genetic Analysis of 400 Patients Refines Understanding and Implicates a New Gene in Atypical Hemolytic Uremic Syndrome.
  found_in:
  - Atypical_Hemolytic_Uremic_Syndrome-deep-research-openscientist.md
  findings:
  - statement: Genetic Analysis of 400 Patients Refines Understanding and Implicates a New Gene in Atypical Hemolytic Uremic Syndrome
    supporting_text: Genetic variation in complement genes is a predisposing factor for atypical hemolytic uremic syndrome (aHUS), a life-threatening thrombotic microangiopathy, however interpreting the effects of genetic variants is challenging and often ambiguous.
- reference: PMID:30711487
  title: Complement Factor H Mutation W1206R Causes Retinal Thrombosis and Ischemic Retinopathy in Mice.
  found_in:
  - Atypical_Hemolytic_Uremic_Syndrome-deep-research-openscientist.md
  findings:
  - statement: '2019 Apr;189(4):826-838. doi: 10.1016/j.ajpath.2019.01.009.'
    supporting_text: '2019 Apr;189(4):826-838. doi: 10.1016/j.ajpath.2019.01.009.'
- reference: PMID:32378251
  title: 'Baseline characteristics of patients with atypical haemolytic uraemic syndrome (aHUS): The Australian cohort in a global aHUS registry.'
  found_in:
  - Atypical_Hemolytic_Uremic_Syndrome-deep-research-openscientist.md
  findings:
  - statement: '2020 Sep;25(9):683-690. doi: 10.1111/nep.13722.'
    supporting_text: '2020 Sep;25(9):683-690. doi: 10.1111/nep.13722.'
- reference: PMID:32877502
  title: Direct activation of the alternative complement pathway by SARS-CoV-2 spike proteins is blocked by factor D inhibition.
  found_in:
  - Atypical_Hemolytic_Uremic_Syndrome-deep-research-openscientist.md
  findings:
  - statement: '2020 Oct 29;136(18):2080-2089. doi: 10.1182/blood.2020008248.'
    supporting_text: '2020 Oct 29;136(18):2080-2089. doi: 10.1182/blood.2020008248.'
- reference: PMID:33712527
  title: IgM Autoantibodies to Complement Factor H in Atypical Hemolytic Uremic Syndrome.
  found_in:
  - Atypical_Hemolytic_Uremic_Syndrome-deep-research-openscientist.md
  findings:
  - statement: Atypical hemolytic uremic syndrome (aHUS), a severe thrombotic microangiopathy, is often related to complement dysregulation, but the pathomechanisms remain unknown in at least 30% of patients.
    supporting_text: Atypical hemolytic uremic syndrome (aHUS), a severe thrombotic microangiopathy, is often related to complement dysregulation, but the pathomechanisms remain unknown in at least 30% of patients.
- reference: PMID:35405682
  title: Mycoplasma pneumoniae Infection Associated with Anti-Factor H Autoantibodies in Atypical Hemolytic Uremic Syndrome.
  found_in:
  - Atypical_Hemolytic_Uremic_Syndrome-deep-research-openscientist.md
  findings:
  - statement: '2022;146(6):593-598. doi: 10.1159/000523998.'
    supporting_text: '2022;146(6):593-598. doi: 10.1159/000523998.'
- reference: PMID:36622444
  title: Variants in complement genes are uncommon in patients with anti-factor H autoantibody-associated atypical hemolytic uremic syndrome.
  found_in:
  - Atypical_Hemolytic_Uremic_Syndrome-deep-research-openscientist.md
  findings:
  - statement: Coexisting genetic variants in patients with anti-factor H (FH)-associated atypical hemolytic uremic syndrome (aHUS) have implications for therapy.
    supporting_text: Coexisting genetic variants in patients with anti-factor H (FH)-associated atypical hemolytic uremic syndrome (aHUS) have implications for therapy.
- reference: PMID:36642429
  title: The Role of Complement in Autoimmune Disease-Associated Thrombotic Microangiopathy and the Potential for Therapeutics.
  found_in:
  - Atypical_Hemolytic_Uremic_Syndrome-deep-research-openscientist.md
  findings:
  - statement: '2023 Jun;50(6):730-740. doi: 10.3899/jrheum.220752.'
    supporting_text: '2023 Jun;50(6):730-740. doi: 10.3899/jrheum.220752.'
- reference: PMID:38604995
  title: 'Characterization of patients with aHUS and associated triggers or clinical conditions: A Global aHUS Registry analysis.'
  found_in:
  - Atypical_Hemolytic_Uremic_Syndrome-deep-research-openscientist.md
  findings:
  - statement: '2024 Aug;29(8):519-527. doi: 10.1111/nep.14304.'
    supporting_text: '2024 Aug;29(8):519-527. doi: 10.1111/nep.14304.'
- reference: PMID:39106497
  title: '[Clinical characteristics and genetic profile of complement system in renal thrombotic microangiopathy in patients with severe forms of arterial hypertension].'
  found_in:
  - Atypical_Hemolytic_Uremic_Syndrome-deep-research-openscientist.md
  findings:
  - statement: The spectrum of diseases characterized by the development of renal thrombotic microangiopathy (TMA) encompasses the malignant hypertension (MHT).
    supporting_text: The spectrum of diseases characterized by the development of renal thrombotic microangiopathy (TMA) encompasses the malignant hypertension (MHT).
- reference: PMID:39291212
  title: Global aHUS Registry Analysis of Patients Switching to Ravulizumab From Eculizumab.
  found_in:
  - Atypical_Hemolytic_Uremic_Syndrome-deep-research-openscientist.md
  findings:
  - statement: '2024 Jun 20;9(9):2648-2656. doi: 10.1016/j.ekir.2024.06.020. eCollection 2024 Sep.'
    supporting_text: '2024 Jun 20;9(9):2648-2656. doi: 10.1016/j.ekir.2024.06.020. eCollection 2024 Sep.'
- reference: DOI:10.5414/CNCS111525
  title: Atypical presentation of H1N1-induced thrombotic microangiopathy with CD46 gene mutation
  found_in:
  - Atypical_Hemolytic_Uremic_Syndrome-deep-research-openscientist.md
  findings:
  - statement: '2025 Mar 14;13:28-36. doi: 10.5414/CNCS111525 . eCollection 2025.'
    supporting_text: '2025 Mar 14;13:28-36. doi: 10.5414/CNCS111525 . eCollection 2025.'
- reference: PMID:40670222
  title: 'Gene-Environment Interaction: Lessons From Complement-Mediated Kidney Disease.'
  found_in:
  - Atypical_Hemolytic_Uremic_Syndrome-deep-research-openscientist.md
  findings:
  - statement: '2025 Jul;45(4):151657. doi: 10.1016/j.semnephrol.2025.151657.'
    supporting_text: '2025 Jul;45(4):151657. doi: 10.1016/j.semnephrol.2025.151657.'
- reference: PMID:40764536
  title: Demographics and baseline disease characteristics of UK patients within the global aHUS registry.
  found_in:
  - Atypical_Hemolytic_Uremic_Syndrome-deep-research-openscientist.md
  findings:
  - statement: '2025 Aug 5;26(1):434. doi: 10.1186/s12882-025-04321-x.'
    supporting_text: '2025 Aug 5;26(1):434. doi: 10.1186/s12882-025-04321-x.'
- reference: PMID:40983966
  title: Identification of a new CD46 gene mutation site in a family with atypical hemolytic uremic syndrome.
  found_in:
  - Atypical_Hemolytic_Uremic_Syndrome-deep-research-openscientist.md
  findings:
  - statement: Atypical hemolytic uremic syndrome (aHUS) is a thrombotic microangiopathy resulting from the dysregulation of the alternative complement pathway.
    supporting_text: Atypical hemolytic uremic syndrome (aHUS) is a thrombotic microangiopathy resulting from the dysregulation of the alternative complement pathway.
- reference: PMID:40996634
  title: Iptacopan/LNP023 and rituximab as rescue therapy in a patient with systemic lupus erythematosus-associated atypical haemolytic uraemic syndrome.
  found_in:
  - Atypical_Hemolytic_Uremic_Syndrome-deep-research-openscientist.md
  findings:
  - statement: '2025 Nov;38(8):2435-2440. doi: 10.1007/s40620-025-02425-z.'
    supporting_text: '2025 Nov;38(8):2435-2440. doi: 10.1007/s40620-025-02425-z.'
- reference: PMID:42133203
  title: A review of genetic and epigenetic biomarkers involved in the occurrence of atypical hemolytic uremic syndrome and its therapeutic strategies.
  found_in: []
  findings:
  - statement: Trials on novel complement inhibitors, regenerative medicine, targeted therapy, and stem cell therapy may also improve future treatment options.
    supporting_text: Trials on novel complement inhibitors, regenerative medicine, targeted therapy, and stem cell therapy may also improve future treatment options.
- reference: PMID:41102576
  title: 'Clinical and genetic characteristics of patients diagnosed with atypical hemolytic uremic syndrome (aHUS): epidemiological data from the Belgian cohort of the Global aHUS Registry.'
  found_in:
  - Atypical_Hemolytic_Uremic_Syndrome-deep-research-openscientist.md
  findings:
  - statement: Atypical hemolytic uremic syndrome (aHUS) usually results from an overactivation of the alternative complement pathway.
    supporting_text: Atypical hemolytic uremic syndrome (aHUS) usually results from an overactivation of the alternative complement pathway.
- reference: PMID:41148448
  title: 'Characteristics and clinical courses of patients with atypical haemolytic uraemic syndrome on dialysis withdrawal after eculizumab treatment: sub-analysis of post-marketing surveillance in Japan.'
  found_in:
  - Atypical_Hemolytic_Uremic_Syndrome-deep-research-openscientist.md
  findings:
  - statement: Atypical haemolytic uraemic syndrome (aHUS) leads to acute kidney injury, necessitating dialysis in about half of patients.
    supporting_text: Atypical haemolytic uraemic syndrome (aHUS) leads to acute kidney injury, necessitating dialysis in about half of patients.
- reference: PMID:41173493
  title: Sustained remission with eculizumab in refractory lupus nephritis with atypical haemolytic uraemic syndrome.
  found_in:
  - Atypical_Hemolytic_Uremic_Syndrome-deep-research-openscientist.md
  findings:
  - statement: '2025 Oct 31;18(10):e266485. doi: 10.1136/bcr-2025-266485.'
    supporting_text: '2025 Oct 31;18(10):e266485. doi: 10.1136/bcr-2025-266485.'
- reference: PMID:41347985
  title: Long-term outcome and management of complement-mediated thrombotic microangiopathy/aHUS.
  found_in:
  - Atypical_Hemolytic_Uremic_Syndrome-deep-research-openscientist.md
  findings:
  - statement: '2025 Dec 5;2025(1):147-153. doi: 10.1182/hematology.2025000700C.'
    supporting_text: '2025 Dec 5;2025(1):147-153. doi: 10.1182/hematology.2025000700C.'
- reference: PMID:41368132
  title: Late Onset Thrombotic Microangiopathy in Kidney Transplants; Poor Outcome Despite Eculizumab Treatment.
  found_in:
  - Atypical_Hemolytic_Uremic_Syndrome-deep-research-openscientist.md
  findings:
  - statement: '2025 Nov 24;38:15404. doi: 10.3389/ti.2025.15404. eCollection 2025.'
    supporting_text: '2025 Nov 24;38:15404. doi: 10.3389/ti.2025.15404. eCollection 2025.'
- reference: PMID:41425686
  title: 'Post-miscarriage Complement-Mediated Thrombotic Microangiopathy in a 27-Year-Old Woman: A Case Highlighting Diagnostic and Therapeutic Gaps in Brazil.'
  found_in:
  - Atypical_Hemolytic_Uremic_Syndrome-deep-research-openscientist.md
  findings:
  - statement: '2025 Dec 20;17(12):e99685. doi: 10.7759/cureus.99685. eCollection 2025 Dec.'
    supporting_text: '2025 Dec 20;17(12):e99685. doi: 10.7759/cureus.99685. eCollection 2025 Dec.'
- reference: PMID:41793014
  title: Clinical Characteristics of 30 Cases of Childhood Haemolytic Uremic Syndrome in a Single Centre.
  found_in:
  - Atypical_Hemolytic_Uremic_Syndrome-deep-research-openscientist.md
  findings:
  - statement: '2026 Mar;31(3):e70181. doi: 10.1111/nep.70181.'
    supporting_text: '2026 Mar;31(3):e70181. doi: 10.1111/nep.70181.'
- reference: DOI:10.1590/2175-8239-jbn-2024-0087en
  title: 'Recommendations for diagnosis and treatment of Atypical Hemolytic Uremic Syndrome (aHUS): an expert consensus statement from the Rare Diseases Committee of the Brazilian Society of Nephrology (COMDORA-SBN)'
  found_in:
  - Atypical_Hemolytic_Uremic_Syndrome-deep-research-falcon.md
  findings: []
- reference: PMID:29907460
  title: Clinical and genetic predictors of atypical hemolytic uremic syndrome phenotype and outcome.
  found_in:
  - Atypical_Hemolytic_Uremic_Syndrome-deep-research-openscientist.md
  findings: []
- reference: PMID:39644051
  title: 'Atypical hemolytic uremic syndrome: diagnosis, management, and discontinuation of therapy.'
  found_in:
  - Atypical_Hemolytic_Uremic_Syndrome-deep-research-openscientist.md
  findings: []
- reference: PMID:39918340
  title: 'Recommendations for diagnosis and treatment of Atypical Hemolytic Uremic Syndrome (aHUS): an expert consensus statement from the Rare Diseases Committee of the Brazilian Society of Nephrology (COMDORA-SBN).'
  found_in:
  - Atypical_Hemolytic_Uremic_Syndrome-deep-research-openscientist.md
  findings: []
- reference: PMID:40217974
  title: 'Atypical Hemolytic Uremic Syndrome: A Review of Complement Dysregulation, Genetic Susceptibility and Multiorgan Involvement.'
  found_in:
  - Atypical_Hemolytic_Uremic_Syndrome-deep-research-openscientist.md
  findings: []

📚

References & Deep Research

References

DOI:10.1007/s00467-024-06480-9

Shiga toxin-producing Escherichia coli infection as a precipitating factor for atypical hemolytic-uremic syndrome

1 finding

Hemolytic uremic syndrome (HUS) is a thrombotic microangiopathy characterized by intravascular hemolysis.

"Hemolytic uremic syndrome (HUS) is a thrombotic microangiopathy characterized by intravascular hemolysis."

DOI:10.1016/j.xkme.2024.100855

Ravulizumab in Atypical Hemolytic Uremic Syndrome: An Analysis of 2-Year Efficacy and Safety Outcomes in 2 Phase 3 Trials

1 finding

Ravulizumab in Atypical Hemolytic Uremic Syndrome: An Analysis of 2-Year Efficacy and Safety Outcomes in 2 Phase 3 Trials

"Ravulizumab in Atypical Hemolytic Uremic Syndrome: An Analysis of 2-Year Efficacy and Safety Outcomes in 2 Phase 3 Trials"

DOI:10.1097/md.0000000000041403

Kidney and pregnancy outcomes in pregnancy-associated atypical hemolytic uremic syndrome: A systematic review and meta-analysis

1 finding

Pregnancy-associated atypical hemolytic uremic syndrome (p-aHUS) is a rare, life-threatening condition characterized by microangiopathic hemolytic anemia, thrombocytopenia, elevated liver enzymes, and acute kidney injury.

"Pregnancy-associated atypical hemolytic uremic syndrome (p-aHUS) is a rare, life-threatening condition characterized by microangiopathic hemolytic anemia, thrombocytopenia, elevated liver enzymes, and acute kidney injury."

DOI:10.1111/ctr.70278

Effectiveness and Safety of Switching to Ravulizumab From Eculizumab in Kidney Transplant Recipients With Atypical Hemolytic Uremic Syndrome: A Global aHUS Registry Analysis

1 finding

Atypical hemolytic uremic syndrome (aHUS) is a disease of complement dysregulation that may lead to kidney failure.

"Atypical hemolytic uremic syndrome (aHUS) is a disease of complement dysregulation that may lead to kidney failure."

DOI:10.1182/hematology.2024000543

Atypical hemolytic uremic syndrome: diagnosis, management, and discontinuation of therapy

1 finding

Atypical hemolytic uremic syndrome: diagnosis, management, and discontinuation of therapy

"Atypical hemolytic uremic syndrome (aHUS) is a thrombotic microangiopathy typically characterized by anemia, thrombocytopenia, and end-organ injury. aHUS occurs due to endothelial injury resulting from overactivation of the alternative pathway of the complement system."

DOI:10.1182/hematology.2025000702

Update in the diagnosis of complement-mediated thrombotic microangiopathy/atypical hemolytic uremic syndrome

1 finding

Complement-mediated thrombotic microangiopathy (C-TMA), also referred to as atypical hemolytic uremic syndrome (aHUS), is a rare but severe cause of microangiopathic hemolysis and organ injury.

"Complement-mediated thrombotic microangiopathy (C-TMA), also referred to as atypical hemolytic uremic syndrome (aHUS), is a rare but severe cause of microangiopathic hemolysis and organ injury."

DOI:10.1186/s12882-025-04080-9

Ten tips for managing complement-mediated thrombotic microangiopathies (formerly atypical hemolytic uremic syndrome): narrative review

1 finding

Ten tips for managing complement-mediated thrombotic microangiopathies (formerly atypical hemolytic uremic syndrome): narrative review

"Ten tips for managing complement-mediated thrombotic microangiopathies (formerly atypical hemolytic uremic syndrome): narrative review"

DOI:10.2147/clep.s245642

Epidemiology of Atypical Hemolytic Uremic Syndrome: A Systematic Literature Review

1 finding

Epidemiology of Atypical Hemolytic Uremic Syndrome: A Systematic Literature Review

"Epidemiology of Atypical Hemolytic Uremic Syndrome: A Systematic Literature Review"

DOI:10.3390/jcm14072527

Atypical Hemolytic Uremic Syndrome: A Review of Complement Dysregulation, Genetic Susceptibility and Multiorgan Involvement

1 finding

Atypical hemolytic uremic syndrome (aHUS) is a rare, life-threatening thrombotic microangiopathy (TMA) characterized by complement dysregulation, leading to microvascular thrombosis and multi-organ injury.

"Atypical hemolytic uremic syndrome (aHUS) is a rare, life-threatening thrombotic microangiopathy (TMA) characterized by complement dysregulation, leading to microvascular thrombosis and multi-organ injury."

PMID:16263173

Localization of the third heparin-binding site in the human complement regulator factor H1.

1 finding

2006 Apr;43(10):1624-32. doi: 10.1016/j.molimm.2005.09.012.

"2006 Apr;43(10):1624-32. doi: 10.1016/j.molimm.2005.09.012."

PMID:17517971

Spontaneous hemolytic uremic syndrome triggered by complement factor H lacking surface recognition domains.

1 finding

2007 Jun 11;204(6):1249-56. doi: 10.1084/jem.20070301.

"2007 Jun 11;204(6):1249-56. doi: 10.1084/jem.20070301."

PMID:21148255

The development of atypical hemolytic uremic syndrome depends on complement C5.

1 finding

2011 Jan;22(1):137-45. doi: 10.1681/ASN.2010050451.

"2011 Jan;22(1):137-45. doi: 10.1681/ASN.2010050451."

PMID:21376430

[Atypical hemolytic-uremic syndrome related to abnormalities within the complement system].

1 finding

2011 Apr;32(4):232-40. doi: 10.1016/j.revmed.2009.09.039.

"2011 Apr;32(4):232-40. doi: 10.1016/j.revmed.2009.09.039."

PMID:28057640

Murine systemic thrombophilia and hemolytic uremic syndrome from a factor H point mutation.

1 finding

2017 Mar 2;129(9):1184-1196. doi: 10.1182/blood-2016-07-728253.

"2017 Mar 2;129(9):1184-1196. doi: 10.1182/blood-2016-07-728253."

PMID:29248304

Glucose-6-Phosphate Dehydrogenase Deficiency Mimicking Atypical Hemolytic Uremic Syndrome.

1 finding

2018 Feb;71(2):287-290. doi: 10.1053/j.ajkd.2017.08.007.

"2018 Feb;71(2):287-290. doi: 10.1053/j.ajkd.2017.08.007."

PMID:29858280

Blocking Properdin Prevents Complement-Mediated Hemolytic Uremic Syndrome and Systemic Thrombophilia.

1 finding

2018 Jul;29(7):1928-1937. doi: 10.1681/ASN.2017121244.

"2018 Jul;29(7):1928-1937. doi: 10.1681/ASN.2017121244."

PMID:30377230

Genetic Analysis of 400 Patients Refines Understanding and Implicates a New Gene in Atypical Hemolytic Uremic Syndrome.

1 finding

Genetic Analysis of 400 Patients Refines Understanding and Implicates a New Gene in Atypical Hemolytic Uremic Syndrome

"Genetic variation in complement genes is a predisposing factor for atypical hemolytic uremic syndrome (aHUS), a life-threatening thrombotic microangiopathy, however interpreting the effects of genetic variants is challenging and often ambiguous."

PMID:30711487

Complement Factor H Mutation W1206R Causes Retinal Thrombosis and Ischemic Retinopathy in Mice.

1 finding

2019 Apr;189(4):826-838. doi: 10.1016/j.ajpath.2019.01.009.

"2019 Apr;189(4):826-838. doi: 10.1016/j.ajpath.2019.01.009."

PMID:32378251

Baseline characteristics of patients with atypical haemolytic uraemic syndrome (aHUS): The Australian cohort in a global aHUS registry.

1 finding

2020 Sep;25(9):683-690. doi: 10.1111/nep.13722.

"2020 Sep;25(9):683-690. doi: 10.1111/nep.13722."

PMID:32877502

Direct activation of the alternative complement pathway by SARS-CoV-2 spike proteins is blocked by factor D inhibition.

1 finding

2020 Oct 29;136(18):2080-2089. doi: 10.1182/blood.2020008248.

"2020 Oct 29;136(18):2080-2089. doi: 10.1182/blood.2020008248."

PMID:33712527

IgM Autoantibodies to Complement Factor H in Atypical Hemolytic Uremic Syndrome.

1 finding

Atypical hemolytic uremic syndrome (aHUS), a severe thrombotic microangiopathy, is often related to complement dysregulation, but the pathomechanisms remain unknown in at least 30% of patients.

"Atypical hemolytic uremic syndrome (aHUS), a severe thrombotic microangiopathy, is often related to complement dysregulation, but the pathomechanisms remain unknown in at least 30% of patients."

PMID:35405682

Mycoplasma pneumoniae Infection Associated with Anti-Factor H Autoantibodies in Atypical Hemolytic Uremic Syndrome.

1 finding

2022;146(6):593-598. doi: 10.1159/000523998.

"2022;146(6):593-598. doi: 10.1159/000523998."

PMID:36622444

Variants in complement genes are uncommon in patients with anti-factor H autoantibody-associated atypical hemolytic uremic syndrome.

1 finding

Coexisting genetic variants in patients with anti-factor H (FH)-associated atypical hemolytic uremic syndrome (aHUS) have implications for therapy.

"Coexisting genetic variants in patients with anti-factor H (FH)-associated atypical hemolytic uremic syndrome (aHUS) have implications for therapy."

PMID:36642429

The Role of Complement in Autoimmune Disease-Associated Thrombotic Microangiopathy and the Potential for Therapeutics.

1 finding

2023 Jun;50(6):730-740. doi: 10.3899/jrheum.220752.

"2023 Jun;50(6):730-740. doi: 10.3899/jrheum.220752."

PMID:38604995

Characterization of patients with aHUS and associated triggers or clinical conditions: A Global aHUS Registry analysis.

1 finding

2024 Aug;29(8):519-527. doi: 10.1111/nep.14304.

"2024 Aug;29(8):519-527. doi: 10.1111/nep.14304."

PMID:39106497

[Clinical characteristics and genetic profile of complement system in renal thrombotic microangiopathy in patients with severe forms of arterial hypertension].

1 finding

The spectrum of diseases characterized by the development of renal thrombotic microangiopathy (TMA) encompasses the malignant hypertension (MHT).

"The spectrum of diseases characterized by the development of renal thrombotic microangiopathy (TMA) encompasses the malignant hypertension (MHT)."

PMID:39291212

Global aHUS Registry Analysis of Patients Switching to Ravulizumab From Eculizumab.

1 finding

2024 Jun 20;9(9):2648-2656. doi: 10.1016/j.ekir.2024.06.020. eCollection 2024 Sep.

"2024 Jun 20;9(9):2648-2656. doi: 10.1016/j.ekir.2024.06.020. eCollection 2024 Sep."

DOI:10.5414/CNCS111525

Atypical presentation of H1N1-induced thrombotic microangiopathy with CD46 gene mutation

1 finding

2025 Mar 14;13:28-36. doi: 10.5414/CNCS111525 . eCollection 2025.

"2025 Mar 14;13:28-36. doi: 10.5414/CNCS111525 . eCollection 2025."

PMID:40670222

Gene-Environment Interaction: Lessons From Complement-Mediated Kidney Disease.

1 finding

2025 Jul;45(4):151657. doi: 10.1016/j.semnephrol.2025.151657.

"2025 Jul;45(4):151657. doi: 10.1016/j.semnephrol.2025.151657."

PMID:40764536

Demographics and baseline disease characteristics of UK patients within the global aHUS registry.

1 finding

2025 Aug 5;26(1):434. doi: 10.1186/s12882-025-04321-x.

"2025 Aug 5;26(1):434. doi: 10.1186/s12882-025-04321-x."

PMID:40983966

Identification of a new CD46 gene mutation site in a family with atypical hemolytic uremic syndrome.

1 finding

Atypical hemolytic uremic syndrome (aHUS) is a thrombotic microangiopathy resulting from the dysregulation of the alternative complement pathway.

"Atypical hemolytic uremic syndrome (aHUS) is a thrombotic microangiopathy resulting from the dysregulation of the alternative complement pathway."

PMID:40996634

Iptacopan/LNP023 and rituximab as rescue therapy in a patient with systemic lupus erythematosus-associated atypical haemolytic uraemic syndrome.

1 finding

2025 Nov;38(8):2435-2440. doi: 10.1007/s40620-025-02425-z.

"2025 Nov;38(8):2435-2440. doi: 10.1007/s40620-025-02425-z."

PMID:42133203

A review of genetic and epigenetic biomarkers involved in the occurrence of atypical hemolytic uremic syndrome and its therapeutic strategies.

1 finding

Trials on novel complement inhibitors, regenerative medicine, targeted therapy, and stem cell therapy may also improve future treatment options.

"Trials on novel complement inhibitors, regenerative medicine, targeted therapy, and stem cell therapy may also improve future treatment options."

PMID:41102576

Clinical and genetic characteristics of patients diagnosed with atypical hemolytic uremic syndrome (aHUS): epidemiological data from the Belgian cohort of the Global aHUS Registry.

1 finding

Atypical hemolytic uremic syndrome (aHUS) usually results from an overactivation of the alternative complement pathway.

"Atypical hemolytic uremic syndrome (aHUS) usually results from an overactivation of the alternative complement pathway."

PMID:41148448

Characteristics and clinical courses of patients with atypical haemolytic uraemic syndrome on dialysis withdrawal after eculizumab treatment: sub-analysis of post-marketing surveillance in Japan.

1 finding

Atypical haemolytic uraemic syndrome (aHUS) leads to acute kidney injury, necessitating dialysis in about half of patients.

"Atypical haemolytic uraemic syndrome (aHUS) leads to acute kidney injury, necessitating dialysis in about half of patients."

PMID:41173493

Sustained remission with eculizumab in refractory lupus nephritis with atypical haemolytic uraemic syndrome.

1 finding

2025 Oct 31;18(10):e266485. doi: 10.1136/bcr-2025-266485.

"2025 Oct 31;18(10):e266485. doi: 10.1136/bcr-2025-266485."

PMID:41347985

Long-term outcome and management of complement-mediated thrombotic microangiopathy/aHUS.

1 finding

2025 Dec 5;2025(1):147-153. doi: 10.1182/hematology.2025000700C.

"2025 Dec 5;2025(1):147-153. doi: 10.1182/hematology.2025000700C."

PMID:41368132

Late Onset Thrombotic Microangiopathy in Kidney Transplants; Poor Outcome Despite Eculizumab Treatment.

1 finding

2025 Nov 24;38:15404. doi: 10.3389/ti.2025.15404. eCollection 2025.

"2025 Nov 24;38:15404. doi: 10.3389/ti.2025.15404. eCollection 2025."

PMID:41425686

Post-miscarriage Complement-Mediated Thrombotic Microangiopathy in a 27-Year-Old Woman: A Case Highlighting Diagnostic and Therapeutic Gaps in Brazil.

1 finding

2025 Dec 20;17(12):e99685. doi: 10.7759/cureus.99685. eCollection 2025 Dec.

"2025 Dec 20;17(12):e99685. doi: 10.7759/cureus.99685. eCollection 2025 Dec."

PMID:41793014

Clinical Characteristics of 30 Cases of Childhood Haemolytic Uremic Syndrome in a Single Centre.

1 finding

2026 Mar;31(3):e70181. doi: 10.1111/nep.70181.

"2026 Mar;31(3):e70181. doi: 10.1111/nep.70181."

DOI:10.1590/2175-8239-jbn-2024-0087en

Recommendations for diagnosis and treatment of Atypical Hemolytic Uremic Syndrome (aHUS): an expert consensus statement from the Rare Diseases Committee of the Brazilian Society of Nephrology (COMDORA-SBN)

No top-level findings curated for this source.

PMID:29907460

Clinical and genetic predictors of atypical hemolytic uremic syndrome phenotype and outcome.

No top-level findings curated for this source.

PMID:39644051

Atypical hemolytic uremic syndrome: diagnosis, management, and discontinuation of therapy.

No top-level findings curated for this source.

PMID:39918340

No top-level findings curated for this source.

PMID:40217974

Atypical Hemolytic Uremic Syndrome: A Review of Complement Dysregulation, Genetic Susceptibility and Multiorgan Involvement.

No top-level findings curated for this source.

Deep Research

Falcon ▸

1. Disease Information (concise overview; current understanding)

Edison Scientific Literature 44 citations 2026-04-22T22:30:33.904504

1. Disease Information (concise overview; current understanding)

Atypical hemolytic uremic syndrome is a complement-mediated thrombotic microangiopathy (TMA) characterized clinically by the triad of microangiopathic hemolytic anemia (MAHA), thrombocytopenia, and end-organ injury—most often acute kidney injury. (java2024atypicalhemolyticuremic pages 1-2, dixon2024ravulizumabinatypical pages 1-2)

Recent clinical reviews emphasize that aHUS is “a prototypical complement-mediated thrombotic microangiopathy (TMA)” and that it occurs due to endothelial injury from overactivation of the alternative complement pathway, driven by either genetic variants or acquired autoantibodies. (java2024atypicalhemolyticuremic pages 1-2)

Direct abstract quote (definition/etiology): - Java (Dec 2024, Hematology): “aHUS occurs due to endothelial injury resulting from overactivation of the alternative pathway of the complement system. The etiology… is either a genetic mutation… or an acquired deficiency due to autoantibodies.” (java2024atypicalhemolyticuremic pages 1-2)

2. Etiology

2.1 Disease causal factors

Primary mechanism: Dysregulated activation of the alternative complement pathway, often conceptualized as impaired regulation of the complement amplification loop (loss-of-function in regulators) or gain-of-function in activators. (java2024atypicalhemolyticuremic pages 1-2, musalem2025tentipsfor pages 1-2)

Genetic vs acquired causes: - Genetic predisposition via variants in complement genes (examples: CFH, CFI, CD46/MCP, C3, CFB, THBD) and complement-related loci (e.g., CFHR rearrangements). (maria2025recommendationsfordiagnosis pages 5-7, java2024atypicalhemolyticuremic pages 1-2) - Acquired predisposition via autoantibodies, especially anti–factor H (anti-FH / anti-CFH) antibodies (often linked to CFHR1–CFHR3 deletions). (java2024atypicalhemolyticuremic pages 1-2, maria2025recommendationsfordiagnosis pages 7-10)

2.2 Risk factors (genetic; triggers as “environmental/clinical exposures”)

Multi-hit model / triggers: Multiple expert sources describe a “double-hit” or “multi-hit” model in which a genetic or acquired complement-control defect often requires a precipitating trigger (e.g., infection, pregnancy, surgery, autoimmune disease, transplantation, certain drugs) to manifest clinically. (cole2025updateinthe pages 1-3, bogdan2025atypicalhemolyticuremic pages 2-4, java2024atypicalhemolyticuremic pages 1-2)

Examples of triggers (from recent review/consensus): infections, pregnancy-related complications, malignancy, autoimmune diseases, surgery, transplantation, and other secondary TMA contexts. (musalem2025tentipsfor pages 1-2, cole2025updateinthe pages 1-3)

2.3 Protective factors

No explicit genetic or environmental protective factors were identified in the retrieved evidence excerpts. (Not available in this run.)

2.4 Gene–environment interaction

The “multi-hit” framing implies gene–environment/clinical interactions: genetically predisposed individuals may remain asymptomatic until an external trigger (infection/pregnancy/surgery/etc.) provokes complement-mediated endothelial injury and TMA. (java2024atypicalhemolyticuremic pages 1-2, bogdan2025atypicalhemolyticuremic pages 2-4)

3. Phenotypes (clinical, laboratory, QoL)

3.1 Core phenotype (TMA triad)

MAHA: anemia with hemolysis markers (elevated LDH, low haptoglobin, schistocytes; Coombs-negative). (maria2025recommendationsfordiagnosis pages 5-7, bogdan2025atypicalhemolyticuremic pages 7-9)
Thrombocytopenia. (java2024atypicalhemolyticuremic pages 1-2, dixon2024ravulizumabinatypical pages 1-2)
Organ injury: most commonly kidney (acute kidney injury, reduced eGFR, creatinine rise), but can be multi-organ. (dixon2024ravulizumabinatypical pages 1-2, bogdan2025atypicalhemolyticuremic pages 5-7)

3.2 Renal phenotype (primary)

Renal involvement is emphasized as predominant: “acute kidney injury is almost always seen,” and may be severe, including dialysis dependence; some presentations can be kidney-limited TMA detectable only by biopsy (with minimal hematologic manifestations). (java2024atypicalhemolyticuremic pages 1-2)

Quantitative renal outcome statements reported in a recent review excerpt include AKI in 60–70% and up to 50% progressing to ESKD, with frequent dialysis/RRT requirement. (bogdan2025atypicalhemolyticuremic pages 4-5)

3.3 Extrarenal manifestations (selected; with frequencies where available)

Evidence supports a broad extrarenal spectrum including neurologic, cardiac, GI, pulmonary, dermatologic, and ocular involvement. (bogdan2025atypicalhemolyticuremic pages 5-7)

Neurologic involvement: reported 8–48% with a registry estimate 27.2%; manifestations include seizures, encephalopathy/altered consciousness, hemiparesis, and visual impairment. (bogdan2025atypicalhemolyticuremic pages 5-7)
Cardiac involvement: in one review excerpt, cardiovascular involvement reported up to 43% in pediatric and 3–10% in adults; includes cardiomyopathy, intracardiac thrombi, and other dysfunction. (bogdan2025atypicalhemolyticuremic pages 4-5)
Pulmonary: respiratory failure requiring mechanical ventilation reported up to 21% in pediatric patients, often secondary to pulmonary edema/fluid overload/cardiac dysfunction. (bogdan2025atypicalhemolyticuremic pages 5-7)
Ocular: ocular involvement reported ~4%, potentially with acute vision loss. (bogdan2025atypicalhemolyticuremic pages 5-7)
Gastrointestinal: diarrhea reported ~50% overall and >80% in anti–factor H antibody-associated aHUS; severe complications can include pancreatitis, GI bleeding, and intestinal perforation. (bogdan2025atypicalhemolyticuremic pages 5-7)

3.4 Quality of life (QoL) impact

aHUS can cause significant functional impairment; Java’s clinical case vignette describes “severe ongoing fatigue requiring assistance with activities of daily living” and inability to work during recovery. (java2024atypicalhemolyticuremic pages 1-2)
In ravulizumab trials, fatigue improvement (FACIT-F) achieved by 26 weeks was maintained through 2 years. (dixon2024ravulizumabinatypical pages 1-2)

3.5 Suggested HPO terms (examples; not exhaustive)

(These are ontology mappings proposed for knowledge-base structuring; they are not asserted to be provided verbatim by the cited papers.) - Hematologic/TMA: Schistocytosis; Hemolytic anemia; Thrombocytopenia. (maria2025recommendationsfordiagnosis pages 5-7, bogdan2025atypicalhemolyticuremic pages 7-9) - Renal: Acute kidney injury; Proteinuria; Hematuria; Hypertension; End-stage renal disease; Dialysis-dependent renal failure. (bogdan2025atypicalhemolyticuremic pages 7-9, bogdan2025atypicalhemolyticuremic pages 4-5) - Neurologic: Seizures; Encephalopathy; Stroke; Altered consciousness. (java2024atypicalhemolyticuremic pages 1-2, bogdan2025atypicalhemolyticuremic pages 5-7) - Cardiac: Cardiomyopathy; Myocardial infarction; Intracardiac thrombosis. (bogdan2025atypicalhemolyticuremic pages 4-5, java2024atypicalhemolyticuremic pages 1-2) - GI: Diarrhea; Pancreatitis; Gastrointestinal hemorrhage. (bogdan2025atypicalhemolyticuremic pages 5-7) - Dermatologic/vascular: Digital gangrene. (java2024atypicalhemolyticuremic pages 1-2)

4. Genetic / Molecular Information

4.1 Causal genes (core set supported in retrieved evidence)

Commonly evaluated genes include CFH, CFI, CD46 (MCP), C3, CFB, CFHR genes (copy-number changes/rearrangements), CFH-CFHR hybrid genes, DGKE, THBD. (maria2025recommendationsfordiagnosis pages 5-7, java2024atypicalhemolyticuremic pages 1-2)

Quantitative genetic architecture: - “Approximately 60–70% of patients with aHUS have identifiable genetic or acquired abnormalities in complement-regulating components,” and genetic mutations are detected in ~60% in one review. (bogdan2025atypicalhemolyticuremic pages 2-4) - VUS findings are common: “In approximately 30% to 40%… a genetic variant of uncertain significance (VUS) may be identified.” (java2024atypicalhemolyticuremic pages 1-2)

4.2 Variant types / functional consequences (high-level)

Loss-of-function in complement regulators (e.g., CFH/CFI/CD46) and gain-of-function in activators (e.g., C3/CFB) are emphasized as etiologic themes. (musalem2025tentipsfor pages 1-2)

4.3 Gene-level frequency estimates (from review excerpts)

CFH: ~20–30% (and in one table range up to ~20–45%). (bogdan2025atypicalhemolyticuremic pages 2-4)
CFI: ~5–10%. (bogdan2025atypicalhemolyticuremic pages 4-5, bogdan2025atypicalhemolyticuremic pages 2-4)
C3: ~2–10%. (bogdan2025atypicalhemolyticuremic pages 2-4)
THBD: ~3–5%. (bogdan2025atypicalhemolyticuremic pages 4-5)
CFB: rare (<1% in one excerpt). (bogdan2025atypicalhemolyticuremic pages 4-5)

4.4 Anti–factor H autoantibodies and CFHR deletions

Anti-FH/anti-CFH autoantibodies: ~10% in US/European cohorts, up to ~50% in some Indian cohorts. (java2024atypicalhemolyticuremic pages 1-2)
Strong association with CFHR1–CFHR3 deletions: one consensus statement cites CFHR1–CFHR3 deletion in 87% of antibody-positive pediatric cases. (maria2025recommendationsfordiagnosis pages 5-7, maria2025recommendationsfordiagnosis pages 7-10)

4.5 Modifier genes / oligogenicity

About 10% of affected patients carry >1 variant or risk polymorphism (supporting additive/oligogenic effects). (java2024atypicalhemolyticuremic pages 1-2)

4.6 Penetrance and expressivity

Overall penetrance of genetic predisposition is reported as ~50%, consistent with trigger dependence. (java2024atypicalhemolyticuremic pages 1-2)
Gene-specific penetrance examples: CFH ~50%, MCP/CD46 ~20% (with MCP often associated with better prognosis). (bogdan2025atypicalhemolyticuremic pages 2-4)

4.7 Epigenetic information / chromosomal abnormalities

No specific epigenetic mechanisms were identified in the retrieved excerpts. (Not available in this run.)

5. Environmental Information (triggers and exposures)

aHUS is not classically caused by a single environmental agent, but multiple clinical exposures can trigger disease in predisposed individuals, including infection and pregnancy-associated complications; malignancy and other inflammatory/immune contexts are described as triggers in CM-TMA literature. (musalem2025tentipsfor pages 1-2, cole2025updateinthe pages 1-3)

Infectious triggers: STEC infection can coexist and may precipitate complement-mediated aHUS in genetically predisposed individuals; thus STEC positivity does not exclude aHUS in atypical/severe courses. (mortari2025shigatoxinproducingescherichia pages 1-2)

Lifestyle/toxin exposures: Not supported by the retrieved evidence excerpts (not asserted).

6. Mechanism / Pathophysiology

6.1 Causal chain (current consensus)

1) Genetic variants or acquired autoantibodies reduce control of the alternative complement pathway amplification loop. (java2024atypicalhemolyticuremic pages 1-2, musalem2025tentipsfor pages 1-2) 2) Uncontrolled complement activation leads to endothelial injury (and downstream microthrombi formation). (java2024atypicalhemolyticuremic pages 1-2) 3) Microvascular thrombosis causes MAHA (shear-related schistocytes), thrombocytopenia (consumption), and ischemic organ injury (kidney predominant). (maria2025recommendationsfordiagnosis pages 5-7)

6.2 Cellular and tissue targets

The proximate site of injury is the microvascular endothelium with consequent small-vessel thrombosis; renal microvasculature and glomerular capillaries are highlighted by renal-dominant clinical manifestations. (maria2025recommendationsfordiagnosis pages 5-7, dixon2024ravulizumabinatypical pages 1-2)

Suggested Cell Ontology (CL) terms (examples): endothelial cell; platelet; erythrocyte (RBC). (maria2025recommendationsfordiagnosis pages 5-7)

Suggested GO biological process terms (examples): complement activation (alternative pathway), regulation of complement activation, platelet aggregation, blood coagulation, endothelial cell injury/activation.

6.3 Biomarkers / functional assays (recent developments)

Because no single definitive diagnostic test exists, emerging functional complement assays are discussed as adjuncts to demonstrate complement hyperactivity (e.g., modified Ham assay and endothelial C5b-9 deposition assays). (cole2025updateinthe pages 1-3)

7. Anatomical Structures Affected

7.1 Organ level (UBERON suggestions)

Kidney (primary): acute kidney injury, proteinuria/hematuria, reduced eGFR; frequent progression to CKD/ESKD in severe cases. (bogdan2025atypicalhemolyticuremic pages 4-5, java2024atypicalhemolyticuremic pages 1-2)
Brain / CNS: seizures, encephalopathy, stroke. (java2024atypicalhemolyticuremic pages 1-2, bogdan2025atypicalhemolyticuremic pages 5-7)
Heart: cardiomyopathy, myocardial infarction, intracardiac thrombi. (bogdan2025atypicalhemolyticuremic pages 4-5, java2024atypicalhemolyticuremic pages 1-2)
Gastrointestinal tract / pancreas / liver: diarrhea, pancreatitis, transaminitis/hepatitis. (bogdan2025atypicalhemolyticuremic pages 5-7, java2024atypicalhemolyticuremic pages 1-2)
Lung: pulmonary edema/respiratory failure in severe cases. (bogdan2025atypicalhemolyticuremic pages 5-7)

7.2 Tissue and cell level

Microvascular beds are implicated (TMA with microvascular occlusion and endothelial injury). (maria2025recommendationsfordiagnosis pages 5-7)

7.3 Subcellular level

Not explicitly described in retrieved excerpts.

8. Temporal Development

8.1 Onset

aHUS can present across the lifespan (pediatric to adult), and onset is often acute/subacute in the setting of a trigger. (bogdan2025atypicalhemolyticuremic pages 2-4, maria2025recommendationsfordiagnosis pages 3-5)

8.2 Progression

Without prompt targeted therapy, disease may progress to chronic kidney disease/ESKD and multi-organ morbidity. (dixon2024ravulizumabinatypical pages 1-2, bogdan2025atypicalhemolyticuremic pages 4-5)

8.3 Relapse/recurrence

Relapse risk is linked to underlying genetic/acquired etiology; long-term discontinuation decisions remain complex and are a focus of hematology guidance. (java2024atypicalhemolyticuremic pages 1-2, musalem2025tentipsfor pages 1-2)

9. Inheritance and Population

9.1 Epidemiology (statistics)

A systematic review of population-based studies reported: - All-ages annual incidence: 0.23–1.9 per million per year. (yan2020epidemiologyofatypical pages 1-2) - ≤20 years annual incidence: 0.26–0.75 per million per year. (yan2020epidemiologyofatypical pages 1-2) - Prevalence ≤20 years: 2.2–9.4 per million; single all-ages prevalence estimate: 4.9 per million. (yan2020epidemiologyofatypical pages 1-2)

Extrarenal complications frequency: extrarenal complications can occur in up to ~20% in some epidemiologic descriptions. (yan2020epidemiologyofatypical pages 1-2, bogdan2025atypicalhemolyticuremic pages 7-9)

9.2 Inheritance pattern

The retrieved evidence supports a genetic predisposition with incomplete penetrance rather than a single uniform Mendelian pattern; both dominant and recessive mechanisms can exist across genes/variants, and acquired autoantibodies also contribute. Because explicit mode(s) of inheritance were not enumerated in the provided excerpts, a detailed AD/AR breakdown is not asserted here. (java2024atypicalhemolyticuremic pages 1-2, bogdan2025atypicalhemolyticuremic pages 2-4)

9.3 Population demographics

Children: roughly equal sex distribution.
Adults: higher female frequency. (yan2020epidemiologyofatypical pages 1-2)

10. Diagnostics

10.1 Clinical tests and biomarkers

Diagnostic work-up centers on confirming TMA and excluding close mimics: - Hemolysis labs: LDH↑, schistocytes, haptoglobin↓, Coombs negative, indirect bilirubin↑. (maria2025recommendationsfordiagnosis pages 5-7) - Platelets decreased; creatinine elevated / AKI. (java2024atypicalhemolyticuremic pages 1-2)

10.2 Differential diagnosis (must exclude)

TTP: exclude using ADAMTS13 activity; severe deficiency (≤10%) supports TTP, while normal/above 10% supports non-TTP TMA context. (maria2025recommendationsfordiagnosis pages 5-7, bogdan2025atypicalhemolyticuremic pages 7-9)
STEC-HUS: exclude using Shiga toxin PCR/stool culture. (maria2025recommendationsfordiagnosis pages 5-7)

10.3 Complement testing (caveats)

Plasma C3 may be low but low C3 occurs in <20%; normal C3 does not rule out aHUS. (maria2025recommendationsfordiagnosis pages 5-7)

10.4 Genetic testing strategy

Expert sources recommend complement gene panel testing plus autoantibody testing in suspected aHUS, including evaluation for CFHR deletions/rearrangements (e.g., by MLPA when NGS is negative) and work-up of VUS by antigenic/functional assays. (java2024atypicalhemolyticuremic pages 1-2, maria2025recommendationsfordiagnosis pages 7-10)

11. Outcome / Prognosis

11.1 Renal outcomes

aHUS can lead to CKD/ESKD without timely treatment; review data cite AKI common and up to 50% ESKD in some cohorts. (bogdan2025atypicalhemolyticuremic pages 4-5)

11.2 Pregnancy-associated aHUS (p-aHUS) outcomes (systematic review/meta-analysis; 2025, searches through Mar 2024)

In 10 studies (386 pregnancies in 380 patients): - Dialysis required: 66.6%. (meena2025kidneyandpregnancy pages 1-2) - ESKD: 25%. (meena2025kidneyandpregnancy pages 1-2) - Maternal mortality: 5%. (meena2025kidneyandpregnancy pages 1-2) - Obstetric complications: preeclampsia 36.4%, HELLP 29.7%. (meena2025kidneyandpregnancy pages 1-2) - Eculizumab benefit: reduced CKD/ESKD risk with pooled risk ratio 0.20 (95% CI 0.09–0.44). (meena2025kidneyandpregnancy pages 1-2)

12. Treatment

12.1 Pharmacotherapy (current standard; real-world implementation)

Terminal complement inhibition (C5 inhibitors): - Eculizumab: effective since approval in 2011; requires q2 week infusions (treatment burden noted). (dixon2024ravulizumabinatypical pages 1-2) - Ravulizumab: next-generation C5 inhibitor designed for extended dosing interval; maintenance every 4–8 weeks weight-based. (dixon2024ravulizumabinatypical pages 1-2)

Ravulizumab 2-year phase 3 outcomes (published online June 14, 2024): - Complete TMA response over 2 years: 61% (C5i-naïve adults) and 90% (C5i-naïve pediatrics). (dixon2024ravulizumabinatypical pages 1-2) - Median eGFR improvement maintained: +35 (adults) and +82.5 mL/min/1.73m² (pediatrics). (dixon2024ravulizumabinatypical pages 1-2) - Safety: “No meningococcal infections were reported” over 2 years; most AEs/SAEs occurred in the first 26 weeks. (dixon2024ravulizumabinatypical pages 1-2)

Real-world registry implementation (kidney transplant recipients switching eculizumab→ravulizumab; data cut Sep 2, 2024; published Aug 2025): - After switching, labs remained stable; no graft failures/rejections reported; in safety population (n=38), 50% had any AE, none treatment-related; no meningococcal infections or deaths reported. (gaeckler2025effectivenessandsafety pages 1-2)

12.2 Supportive care / plasma exchange

Plasma exchange historically served as primary therapy in the pre-C5 inhibitor era, and remains relevant particularly in anti–factor H autoantibody–associated disease (often combined with immunosuppression), while prompt complement inhibition is emphasized for complement-driven disease. (musalem2025tentipsfor pages 1-2)

12.3 Prevention / prophylaxis related to therapy

Prophylactic measures against infections—particularly meningococcal disease—are described as mandatory/required for patients receiving C5 inhibitors. (musalem2025tentipsfor pages 1-2)

12.4 Suggested MAXO terms (examples)

Complement inhibitor therapy; monoclonal antibody therapy; plasma exchange (therapeutic apheresis); kidney replacement therapy (dialysis); kidney transplantation; vaccination (meningococcal).

13. Prevention

Primary prevention of genetically predisposed aHUS is not established in the retrieved evidence. Prevention is primarily tertiary in practice (prevent relapse/complications) via appropriate complement inhibition strategies, infection prophylaxis/vaccination for C5 blockade, and trigger management (e.g., pregnancy-associated risk planning, transplant risk stratification). (musalem2025tentipsfor pages 1-2, gaeckler2025effectivenessandsafety pages 1-2)

14. Other Species / Natural Disease

Not available from retrieved sources in this run; no claims made.

15. Model Organisms

Not available from retrieved sources in this run; no claims made.

Recent developments and 2023–2024 highlights (prioritized)

2024 ASH Hematology review (Java, Dec 2024) emphasizes systematic genetic/autoantibody testing, high VUS rate (30–40%), and clinical stratification for discontinuation decisions. (java2024atypicalhemolyticuremic pages 1-2)
2024 Kidney Medicine phase 3 long-term analysis (Dixon et al., published online Jun 14, 2024) provides durable 2-year efficacy/safety and sustained QoL improvements for ravulizumab in adults and children. (dixon2024ravulizumabinatypical pages 1-2)

Summary statistics and key points table

The following table consolidates high-yield identifiers, diagnostic criteria, genetic architecture, epidemiology, and treatment outcomes.

Category	Data point	Value/Statement	Source (first author, year)	URL	Evidence citation id (pqac-...)
Definition	Core disease definition	aHUS/complement-mediated TMA is a rare, severe thrombotic microangiopathy driven by dysregulated alternative complement pathway activation, typically presenting with microangiopathic hemolytic anemia (MAHA), thrombocytopenia, and organ injury.	Cole, 2025	https://doi.org/10.1182/hematology.2025000702	(cole2025updateinthe pages 1-3)
Definition	TMA triad	Clinical suspicion is based on the TMA triad: MAHA + thrombocytopenia + organ damage/acute kidney injury; kidneys are most commonly affected but multiorgan disease occurs.	Bogdan, 2025	https://doi.org/10.3390/jcm14072527	(bogdan2025atypicalhemolyticuremic pages 1-2, bogdan2025atypicalhemolyticuremic pages 7-9)
Diagnosis	Exclude TTP	TTP should be rapidly excluded; severe ADAMTS13 deficiency (≤10%) supports TTP, while aHUS is more likely when ADAMTS13 is >10%.	Bogdan, 2025	https://doi.org/10.3390/jcm14072527	(bogdan2025atypicalhemolyticuremic pages 5-7, bogdan2025atypicalhemolyticuremic pages 7-9)
Diagnosis	Exclude STEC-HUS	STEC-HUS should be excluded using Shiga toxin testing (stool PCR/culture/serology as available); aHUS diagnosis is one of exclusion.	Maria, 2025	https://doi.org/10.1590/2175-8239-jbn-2024-0087en	(maria2025recommendationsfordiagnosis pages 5-7, maria2025recommendationsfordiagnosis pages 3-5)
Diagnosis	Typical hemolysis/lab features	Supportive findings include schistocytes, elevated LDH, low haptoglobin, negative direct Coombs test, indirect hyperbilirubinemia, hemoglobinuria, and often AKI.	Bogdan, 2025	https://doi.org/10.3390/jcm14072527	(bogdan2025atypicalhemolyticuremic pages 7-9)
Genetics	Overall genetic/acquired basis	Approximately 60–70% of patients have identifiable genetic or acquired abnormalities in complement-regulating components; genetic mutations are detected in roughly 60% of cases.	Bogdan, 2025	https://doi.org/10.3390/jcm14072527	(bogdan2025atypicalhemolyticuremic pages 2-4)
Genetics	Genetic basis phrasing from consensus	A genetic basis is present in nearly two-thirds of aHUS cases.	Maria, 2025	https://doi.org/10.1590/2175-8239-jbn-2024-0087en	(maria2025recommendationsfordiagnosis pages 5-7, maria2025recommendationsfordiagnosis pages 7-10)
Genetics	Major genes implicated	Commonly implicated genes include CFH, CFI, CD46/MCP, C3, CFB, THBD, DGKE, and CFHR rearrangements/deletions; anti-CFH autoimmunity is an important acquired mechanism.	Java, 2024	https://doi.org/10.1182/hematology.2024000543	(java2024atypicalhemolyticuremic pages 1-2)
Genetics	CFH frequency	CFH variants are the most common, accounting for about 20–30% of cases (some reports/tables up to ~20–45%).	Bogdan, 2025	https://doi.org/10.3390/jcm14072527	(bogdan2025atypicalhemolyticuremic pages 2-4)
Genetics	CFI frequency	CFI variants account for about 5–10% of cases.	Bogdan, 2025	https://doi.org/10.3390/jcm14072527	(bogdan2025atypicalhemolyticuremic pages 4-5, bogdan2025atypicalhemolyticuremic pages 2-4)
Genetics	C3 frequency	C3 variants account for about 2–10% of cases.	Bogdan, 2025	https://doi.org/10.3390/jcm14072527	(bogdan2025atypicalhemolyticuremic pages 2-4)
Genetics	Other gene frequencies	CFB variants are rare (<1% in one review excerpt); THBD variants ~3–5%.	Bogdan, 2025	https://doi.org/10.3390/jcm14072527	(bogdan2025atypicalhemolyticuremic pages 4-5)
Genetics	Penetrance examples	Estimated penetrance varies by gene: CFH ~50%; MCP/CD46 ~20%, with MCP often associated with better prognosis and lower post-transplant recurrence risk.	Bogdan, 2025	https://doi.org/10.3390/jcm14072527	(bogdan2025atypicalhemolyticuremic pages 2-4)
Genetics	Multi-hit model	Penetrance is incomplete (~50% overall in one review), consistent with a multi-hit model requiring triggers such as infection, pregnancy, surgery, autoimmune disease, or transplantation.	Java, 2024	https://doi.org/10.1182/hematology.2024000543	(java2024atypicalhemolyticuremic pages 1-2, bogdan2025atypicalhemolyticuremic pages 2-4)
Genetics	Anti-factor H autoantibody prevalence	Anti-FH/anti-CFH autoantibodies occur in ~10% of US/European cohorts, affect ~10–15% of pediatric aHUS in some reviews, and may reach ~50% in some Indian cohorts.	Java, 2024	https://doi.org/10.1182/hematology.2024000543	(bogdan2025atypicalhemolyticuremic pages 4-5, java2024atypicalhemolyticuremic pages 1-2)
Genetics	CFHR deletion association	Anti-CFH autoantibodies are strongly associated with homozygous CFHR1-CFHR3 deletions; one consensus cited this deletion in 87% of antibody-positive pediatric cases.	Maria, 2025	https://doi.org/10.1590/2175-8239-jbn-2024-0087en	(maria2025recommendationsfordiagnosis pages 5-7, maria2025recommendationsfordiagnosis pages 7-10)
Diagnosis	Complement C3 level caveat	Low plasma C3 is found in fewer than 20% of patients; normal C3 does not exclude aHUS.	Maria, 2025	https://doi.org/10.1590/2175-8239-jbn-2024-0087en	(maria2025recommendationsfordiagnosis pages 5-7)
Epidemiology	Overall incidence	Annual all-ages incidence in the literature ranges from 0.23 to 1.9 per million population.	Yan, 2020	https://doi.org/10.2147/CLEP.S245642	(yan2020epidemiologyofatypical pages 3-5, yan2020epidemiologyofatypical pages 1-2)
Epidemiology	Pediatric incidence	Annual incidence in individuals ≤20 years ranges from 0.26 to 0.75 per million.	Yan, 2020	https://doi.org/10.2147/CLEP.S245642	(yan2020epidemiologyofatypical pages 3-5, yan2020epidemiologyofatypical pages 1-2)
Epidemiology	Prevalence	Prevalence in individuals ≤20 years ranges from 2.2 to 9.4 per million; one all-ages prevalence estimate was 4.9 per million.	Yan, 2020	https://doi.org/10.2147/CLEP.S245642	(yan2020epidemiologyofatypical pages 3-5, yan2020epidemiologyofatypical pages 1-2)
Epidemiology	Demographics	Children show roughly equal sex distribution; adults show higher female frequency. Mean/median diagnosis age is typically <2 years in pediatric reports and ~31–37 years in adults.	Yan, 2020	https://doi.org/10.2147/CLEP.S245642	(yan2020epidemiologyofatypical pages 3-5, yan2020epidemiologyofatypical pages 1-2)
Treatment	Approved complement target	C5 is a validated therapeutic target; FDA/clinical development evidence includes eculizumab and ravulizumab, with additional phase 3 development for crovalimab.	Open Targets, accessed via platform evidence	https://platform.opentargets.org/disease/MONDO_0016244/associations	(dixon2024ravulizumabinatypical pages 1-2)
Treatment	Ravulizumab 2-year complete TMA response	In phase 3 trials, 2-year complete TMA response rates were 61% in C5 inhibitor-naive adults and 90% in pediatric patients.	Dixon, 2024	https://doi.org/10.1016/j.xkme.2024.100855	(dixon2024ravulizumabinatypical pages 1-2, dixon2024ravulizumabinatypical pages 9-10)
Treatment	Ravulizumab renal benefit	Median eGFR improvement at 2 years was +35 mL/min/1.73 m² in adults and +82.5 mL/min/1.73 m² in pediatric patients.	Dixon, 2024	https://doi.org/10.1016/j.xkme.2024.100855	(dixon2024ravulizumabinatypical pages 1-2)
Treatment	Ravulizumab safety highlights	Most AEs/SAEs occurred in the first 26 weeks and declined thereafter; no meningococcal infections were reported over 2 years. Common adult AEs included headache (40%) and diarrhea (35%).	Dixon, 2024	https://doi.org/10.1016/j.xkme.2024.100855	(dixon2024ravulizumabinatypical pages 9-10, dixon2024ravulizumabinatypical pages 5-6)
Treatment	Ravulizumab dosing practicality	Ravulizumab provides immediate, complete, sustained C5 inhibition with maintenance dosing every 4–8 weeks by weight.	Dixon, 2024	https://doi.org/10.1016/j.xkme.2024.100855	(dixon2024ravulizumabinatypical pages 1-2, dixon2024ravulizumabinatypical pages 9-10)
Treatment	Real-world switch: transplant recipients	In Global aHUS Registry kidney transplant recipients switched from eculizumab to ravulizumab, labs remained stable, with no TMA signs/symptoms, no dialysis, and no transplant rejection/graft failure reported after switching.	Gaeckler, 2025	https://doi.org/10.1111/ctr.70278	(gaeckler2025effectivenessandsafety pages 1-2, gaeckler2025effectivenessandsafety pages 2-3)
Treatment	Real-world switch safety	In the registry safety population (n=38), 23 AEs occurred in 19 patients (50.0%), none treatment-related; no meningococcal infections or deaths were reported.	Gaeckler, 2025	https://doi.org/10.1111/ctr.70278	(gaeckler2025effectivenessandsafety pages 1-2)
Pregnancy-associated aHUS	Disease burden in meta-analysis	Systematic review/meta-analysis included 386 pregnancies in 380 patients with pregnancy-associated aHUS.	Meena, 2025	https://doi.org/10.1097/MD.0000000000041403	(meena2025kidneyandpregnancy pages 1-2, meena2025kidneyandpregnancy pages 3-4)
Pregnancy-associated aHUS	Dialysis requirement	228/342 patients (66.6%) required dialysis.	Meena, 2025	https://doi.org/10.1097/MD.0000000000041403	(meena2025kidneyandpregnancy pages 2-3, meena2025kidneyandpregnancy pages 1-2)
Pregnancy-associated aHUS	ESKD proportion	About 25% developed ESKD.	Meena, 2025	https://doi.org/10.1097/MD.0000000000041403	(meena2025kidneyandpregnancy pages 2-3, meena2025kidneyandpregnancy pages 1-2)
Pregnancy-associated aHUS	CKD/persistent dysfunction	Persistent renal dysfunction/CKD was reported in about 20% of patients.	Meena, 2025	https://doi.org/10.1097/MD.0000000000041403	(meena2025kidneyandpregnancy pages 2-3)
Pregnancy-associated aHUS	Maternal mortality	Maternal deaths occurred in 5% of reported cases.	Meena, 2025	https://doi.org/10.1097/MD.0000000000041403	(meena2025kidneyandpregnancy pages 2-3, meena2025kidneyandpregnancy pages 1-2)
Pregnancy-associated aHUS	Obstetric complications	Preeclampsia occurred in 36.4% and HELLP syndrome in 29.7% of reported patients.	Meena, 2025	https://doi.org/10.1097/MD.0000000000041403	(meena2025kidneyandpregnancy pages 2-3, meena2025kidneyandpregnancy pages 1-2)
Pregnancy-associated aHUS	Eculizumab effect estimate (CKD/ESKD)	Eculizumab significantly reduced poor renal outcomes; pooled risk ratio/odds ratio for CKD/ESKD was 0.20 (95% CI 0.09–0.44), with low heterogeneity.	Meena, 2025	https://doi.org/10.1097/MD.0000000000041403	(meena2025kidneyandpregnancy pages 1-2, meena2025kidneyandpregnancy pages 3-4)
Pregnancy-associated aHUS	Eculizumab effect estimate (ESKD)	Unadjusted hazard ratio for ESKD with eculizumab was 0.14 (95% CI 0.04–0.47; P=.002) in the meta-analysis synthesis.	Meena, 2025	https://doi.org/10.1097/MD.0000000000041403	(meena2025kidneyandpregnancy pages 3-4)
Pregnancy-associated aHUS	Mortality/safety signal with eculizumab	Meta-analysis described a significant mortality benefit and reported no allergic reactions, infections, drug-related deaths, or fetal congenital abnormalities attributed to eculizumab in included studies.	Meena, 2025	https://doi.org/10.1097/MD.0000000000041403	(meena2025kidneyandpregnancy pages 7-9)

Table: This table compiles high-yield clinical, genetic, epidemiologic, treatment, and pregnancy-associated statistics for atypical hemolytic uremic syndrome from the gathered evidence. It is designed as a compact reference for a disease knowledge base or research summary.

Limitations of this evidence package

ICD-10/ICD-11, Orphanet ORPHA, and OMIM identifiers were not explicitly present in the retrieved excerpts; therefore they are not asserted despite being likely available in external disease resources.
Dedicated model-organism/animal-model primary literature was not retrieved in this run; therefore model organism sections are intentionally left as “not available.”

References

(musalem2025tentipsfor pages 1-2): Pilar Musalem. Ten tips for managing complement-mediated thrombotic microangiopathies (formerly atypical hemolytic uremic syndrome): narrative review. BMC Nephrology, Mar 2025. URL: https://doi.org/10.1186/s12882-025-04080-9, doi:10.1186/s12882-025-04080-9. This article has 3 citations and is from a peer-reviewed journal.
(cole2025updateinthe pages 1-3): Michael Arthur Cole. Update in the diagnosis of complement-mediated thrombotic microangiopathy/atypical hemolytic uremic syndrome. Hematology, 2025:164-175, Dec 2025. URL: https://doi.org/10.1182/hematology.2025000702, doi:10.1182/hematology.2025000702. This article has 2 citations and is from a peer-reviewed journal.
(bogdan2025atypicalhemolyticuremic pages 2-4): Razvan-George Bogdan, Paula Anderco, Cristian Ichim, Anca-Maria Cimpean, Samuel Bogdan Todor, Mihai Glaja-Iliescu, Zorin Petrisor Crainiceanu, and Mirela Livia Popa. Atypical hemolytic uremic syndrome: a review of complement dysregulation, genetic susceptibility and multiorgan involvement. Journal of Clinical Medicine, 14:2527, Apr 2025. URL: https://doi.org/10.3390/jcm14072527, doi:10.3390/jcm14072527. This article has 18 citations.
(dixon2024ravulizumabinatypical pages 1-2): Bradley P. Dixon, David Kavanagh, Alvaro Domingo Madrid Aris, Brigitte Adams, Hee Gyung Kang, Edward Wang, Katherine Garlo, Masayo Ogawa, Praveen Amancha, Sourish Chakravarty, Nils Heyne, Seong Heon Kim, Spero Cataland, Sung-Soo Yoon, Yoshitaka Miyakawa, Yosu Luque, Melissa Muff-Luett, Kazuki Tanaka, and Larry A. Greenbaum. Ravulizumab in atypical hemolytic uremic syndrome: an analysis of 2-year efficacy and safety outcomes in 2 phase 3 trials. Kidney Medicine, 6:100855, Aug 2024. URL: https://doi.org/10.1016/j.xkme.2024.100855, doi:10.1016/j.xkme.2024.100855. This article has 27 citations.
(NCT01522183 chunk 5): Atypical Hemolytic-Uremic Syndrome (aHUS) Registry. Alexion Pharmaceuticals, Inc.. 2013. ClinicalTrials.gov Identifier: NCT01522183
(NCT04861259 chunk 3): A Study Evaluating the Efficacy, Safety, Pharmacokinetics and Pharmacodynamics of Crovalimab in Adult and Adolescent Participants With Atypical Hemolytic Uremic Syndrome (aHUS). Hoffmann-La Roche. 2021. ClinicalTrials.gov Identifier: NCT04861259
(java2024atypicalhemolyticuremic pages 1-2): Anuja Java. Atypical hemolytic uremic syndrome: diagnosis, management, and discontinuation of therapy. Hematology, 2024:200-205, Dec 2024. URL: https://doi.org/10.1182/hematology.2024000543, doi:10.1182/hematology.2024000543. This article has 15 citations and is from a peer-reviewed journal.
(cole2025updateinthe pages 12-12): Michael Arthur Cole. Update in the diagnosis of complement-mediated thrombotic microangiopathy/atypical hemolytic uremic syndrome. Hematology, 2025:164-175, Dec 2025. URL: https://doi.org/10.1182/hematology.2025000702, doi:10.1182/hematology.2025000702. This article has 2 citations and is from a peer-reviewed journal.
(meena2025kidneyandpregnancy pages 1-2): Priti Meena, Ruju Gala, Rashmi Ranjan Das, Vinant Bhargava, Yellampalli Saivani, Sandip Panda, Alok Mantri, and Krishna Kumar Agrawaal. Kidney and pregnancy outcomes in pregnancy-associated atypical hemolytic uremic syndrome: a systematic review and meta-analysis. Medicine, 104:e41403, Jan 2025. URL: https://doi.org/10.1097/md.0000000000041403, doi:10.1097/md.0000000000041403. This article has 9 citations and is from a peer-reviewed journal.
(yan2020epidemiologyofatypical pages 3-5): Kevin Yan, Kamal Desai, Lakshmi Gullapalli, Eric Druyts, and Chakrapani Balijepalli. Epidemiology of atypical hemolytic uremic syndrome: a systematic literature review. Clinical Epidemiology, 12:295-305, Mar 2020. URL: https://doi.org/10.2147/clep.s245642, doi:10.2147/clep.s245642. This article has 144 citations and is from a highest quality peer-reviewed journal.
(maria2025recommendationsfordiagnosis pages 5-7): Helena Vaisbich Maria, Andrade Luis Gustavo Modelli de, Barbosa Maria Izabel Neves de Holan da, Castro Maria Cristina Ribeiro de, Miranda Silvana Maria Carvalho, Poli-de-Figueiredo Carlos Eduardo, Araujo Stanley de Almeida, Neto Miguel Ernandes, Penido Maria Goretti Moreira Guimarães, Sobral Roberta Mendes Lima, Neto Oreste Ferra, Neves Precil Diego Miranda de Menezes, Silva Cassiano Augusto Braga da, Barreto Fellype Carvalho, Pietrobom Igor Gouveia, and Palma Lilian Monteiro Pereira. Recommendations for diagnosis and treatment of atypical hemolytic uremic syndrome (ahus): an expert consensus statement from the rare diseases committee of the brazilian society of nephrology (comdora-sbn). Jornal Brasileiro de Nefrologia, Feb 2025. URL: https://doi.org/10.1590/2175-8239-jbn-2024-0087en, doi:10.1590/2175-8239-jbn-2024-0087en. This article has 7 citations.
(maria2025recommendationsfordiagnosis pages 7-10): Helena Vaisbich Maria, Andrade Luis Gustavo Modelli de, Barbosa Maria Izabel Neves de Holan da, Castro Maria Cristina Ribeiro de, Miranda Silvana Maria Carvalho, Poli-de-Figueiredo Carlos Eduardo, Araujo Stanley de Almeida, Neto Miguel Ernandes, Penido Maria Goretti Moreira Guimarães, Sobral Roberta Mendes Lima, Neto Oreste Ferra, Neves Precil Diego Miranda de Menezes, Silva Cassiano Augusto Braga da, Barreto Fellype Carvalho, Pietrobom Igor Gouveia, and Palma Lilian Monteiro Pereira. Recommendations for diagnosis and treatment of atypical hemolytic uremic syndrome (ahus): an expert consensus statement from the rare diseases committee of the brazilian society of nephrology (comdora-sbn). Jornal Brasileiro de Nefrologia, Feb 2025. URL: https://doi.org/10.1590/2175-8239-jbn-2024-0087en, doi:10.1590/2175-8239-jbn-2024-0087en. This article has 7 citations.
(bogdan2025atypicalhemolyticuremic pages 7-9): Razvan-George Bogdan, Paula Anderco, Cristian Ichim, Anca-Maria Cimpean, Samuel Bogdan Todor, Mihai Glaja-Iliescu, Zorin Petrisor Crainiceanu, and Mirela Livia Popa. Atypical hemolytic uremic syndrome: a review of complement dysregulation, genetic susceptibility and multiorgan involvement. Journal of Clinical Medicine, 14:2527, Apr 2025. URL: https://doi.org/10.3390/jcm14072527, doi:10.3390/jcm14072527. This article has 18 citations.
(bogdan2025atypicalhemolyticuremic pages 5-7): Razvan-George Bogdan, Paula Anderco, Cristian Ichim, Anca-Maria Cimpean, Samuel Bogdan Todor, Mihai Glaja-Iliescu, Zorin Petrisor Crainiceanu, and Mirela Livia Popa. Atypical hemolytic uremic syndrome: a review of complement dysregulation, genetic susceptibility and multiorgan involvement. Journal of Clinical Medicine, 14:2527, Apr 2025. URL: https://doi.org/10.3390/jcm14072527, doi:10.3390/jcm14072527. This article has 18 citations.
(bogdan2025atypicalhemolyticuremic pages 4-5): Razvan-George Bogdan, Paula Anderco, Cristian Ichim, Anca-Maria Cimpean, Samuel Bogdan Todor, Mihai Glaja-Iliescu, Zorin Petrisor Crainiceanu, and Mirela Livia Popa. Atypical hemolytic uremic syndrome: a review of complement dysregulation, genetic susceptibility and multiorgan involvement. Journal of Clinical Medicine, 14:2527, Apr 2025. URL: https://doi.org/10.3390/jcm14072527, doi:10.3390/jcm14072527. This article has 18 citations.
(mortari2025shigatoxinproducingescherichia pages 1-2): Gabriele Mortari, Carolina Bigatti, Giulia Proietti Gaffi, Barbara Lionetti, Andrea Angeletti, Simona Matarese, Enrico Eugenio Verrina, Gianluca Caridi, Francesca Lugani, Valerio Gaetano Vellone, Decimo Silvio Chiarenza, and Edoardo La Porta. Shiga toxin-producing escherichia coli infection as a precipitating factor for atypical hemolytic-uremic syndrome. Pediatric Nephrology (Berlin, Germany), 40:449-461, Sep 2025. URL: https://doi.org/10.1007/s00467-024-06480-9, doi:10.1007/s00467-024-06480-9. This article has 2 citations.
(maria2025recommendationsfordiagnosis pages 3-5): Helena Vaisbich Maria, Andrade Luis Gustavo Modelli de, Barbosa Maria Izabel Neves de Holan da, Castro Maria Cristina Ribeiro de, Miranda Silvana Maria Carvalho, Poli-de-Figueiredo Carlos Eduardo, Araujo Stanley de Almeida, Neto Miguel Ernandes, Penido Maria Goretti Moreira Guimarães, Sobral Roberta Mendes Lima, Neto Oreste Ferra, Neves Precil Diego Miranda de Menezes, Silva Cassiano Augusto Braga da, Barreto Fellype Carvalho, Pietrobom Igor Gouveia, and Palma Lilian Monteiro Pereira. Recommendations for diagnosis and treatment of atypical hemolytic uremic syndrome (ahus): an expert consensus statement from the rare diseases committee of the brazilian society of nephrology (comdora-sbn). Jornal Brasileiro de Nefrologia, Feb 2025. URL: https://doi.org/10.1590/2175-8239-jbn-2024-0087en, doi:10.1590/2175-8239-jbn-2024-0087en. This article has 7 citations.
(yan2020epidemiologyofatypical pages 1-2): Kevin Yan, Kamal Desai, Lakshmi Gullapalli, Eric Druyts, and Chakrapani Balijepalli. Epidemiology of atypical hemolytic uremic syndrome: a systematic literature review. Clinical Epidemiology, 12:295-305, Mar 2020. URL: https://doi.org/10.2147/clep.s245642, doi:10.2147/clep.s245642. This article has 144 citations and is from a highest quality peer-reviewed journal.
(gaeckler2025effectivenessandsafety pages 1-2): Anja Gaeckler, Imad Al‐Dakkak, Nuria Saval, Hans Herman Dieperink, Margriet Eygenraam, Larry A. Greenbaum, Nicole Isbel, and Johan Vande Walle. Effectiveness and safety of switching to ravulizumab from eculizumab in kidney transplant recipients with atypical hemolytic uremic syndrome: a global ahus registry analysis. Clinical Transplantation, Aug 2025. URL: https://doi.org/10.1111/ctr.70278, doi:10.1111/ctr.70278. This article has 2 citations and is from a peer-reviewed journal.
(bogdan2025atypicalhemolyticuremic pages 1-2): Razvan-George Bogdan, Paula Anderco, Cristian Ichim, Anca-Maria Cimpean, Samuel Bogdan Todor, Mihai Glaja-Iliescu, Zorin Petrisor Crainiceanu, and Mirela Livia Popa. Atypical hemolytic uremic syndrome: a review of complement dysregulation, genetic susceptibility and multiorgan involvement. Journal of Clinical Medicine, 14:2527, Apr 2025. URL: https://doi.org/10.3390/jcm14072527, doi:10.3390/jcm14072527. This article has 18 citations.
(dixon2024ravulizumabinatypical pages 9-10): Bradley P. Dixon, David Kavanagh, Alvaro Domingo Madrid Aris, Brigitte Adams, Hee Gyung Kang, Edward Wang, Katherine Garlo, Masayo Ogawa, Praveen Amancha, Sourish Chakravarty, Nils Heyne, Seong Heon Kim, Spero Cataland, Sung-Soo Yoon, Yoshitaka Miyakawa, Yosu Luque, Melissa Muff-Luett, Kazuki Tanaka, and Larry A. Greenbaum. Ravulizumab in atypical hemolytic uremic syndrome: an analysis of 2-year efficacy and safety outcomes in 2 phase 3 trials. Kidney Medicine, 6:100855, Aug 2024. URL: https://doi.org/10.1016/j.xkme.2024.100855, doi:10.1016/j.xkme.2024.100855. This article has 27 citations.
(dixon2024ravulizumabinatypical pages 5-6): Bradley P. Dixon, David Kavanagh, Alvaro Domingo Madrid Aris, Brigitte Adams, Hee Gyung Kang, Edward Wang, Katherine Garlo, Masayo Ogawa, Praveen Amancha, Sourish Chakravarty, Nils Heyne, Seong Heon Kim, Spero Cataland, Sung-Soo Yoon, Yoshitaka Miyakawa, Yosu Luque, Melissa Muff-Luett, Kazuki Tanaka, and Larry A. Greenbaum. Ravulizumab in atypical hemolytic uremic syndrome: an analysis of 2-year efficacy and safety outcomes in 2 phase 3 trials. Kidney Medicine, 6:100855, Aug 2024. URL: https://doi.org/10.1016/j.xkme.2024.100855, doi:10.1016/j.xkme.2024.100855. This article has 27 citations.
(gaeckler2025effectivenessandsafety pages 2-3): Anja Gaeckler, Imad Al‐Dakkak, Nuria Saval, Hans Herman Dieperink, Margriet Eygenraam, Larry A. Greenbaum, Nicole Isbel, and Johan Vande Walle. Effectiveness and safety of switching to ravulizumab from eculizumab in kidney transplant recipients with atypical hemolytic uremic syndrome: a global ahus registry analysis. Clinical Transplantation, Aug 2025. URL: https://doi.org/10.1111/ctr.70278, doi:10.1111/ctr.70278. This article has 2 citations and is from a peer-reviewed journal.
(meena2025kidneyandpregnancy pages 3-4): Priti Meena, Ruju Gala, Rashmi Ranjan Das, Vinant Bhargava, Yellampalli Saivani, Sandip Panda, Alok Mantri, and Krishna Kumar Agrawaal. Kidney and pregnancy outcomes in pregnancy-associated atypical hemolytic uremic syndrome: a systematic review and meta-analysis. Medicine, 104:e41403, Jan 2025. URL: https://doi.org/10.1097/md.0000000000041403, doi:10.1097/md.0000000000041403. This article has 9 citations and is from a peer-reviewed journal.
(meena2025kidneyandpregnancy pages 2-3): Priti Meena, Ruju Gala, Rashmi Ranjan Das, Vinant Bhargava, Yellampalli Saivani, Sandip Panda, Alok Mantri, and Krishna Kumar Agrawaal. Kidney and pregnancy outcomes in pregnancy-associated atypical hemolytic uremic syndrome: a systematic review and meta-analysis. Medicine, 104:e41403, Jan 2025. URL: https://doi.org/10.1097/md.0000000000041403, doi:10.1097/md.0000000000041403. This article has 9 citations and is from a peer-reviewed journal.
(meena2025kidneyandpregnancy pages 7-9): Priti Meena, Ruju Gala, Rashmi Ranjan Das, Vinant Bhargava, Yellampalli Saivani, Sandip Panda, Alok Mantri, and Krishna Kumar Agrawaal. Kidney and pregnancy outcomes in pregnancy-associated atypical hemolytic uremic syndrome: a systematic review and meta-analysis. Medicine, 104:e41403, Jan 2025. URL: https://doi.org/10.1097/md.0000000000041403, doi:10.1097/md.0000000000041403. This article has 9 citations and is from a peer-reviewed journal.

OpenScientist ▸

Key Findings

openscientist-autonomous 34 citations 2026-05-05T08:06:37.384502

Key Findings

Finding 1: aHUS Is Caused by Dysregulation of the Alternative Complement Pathway

Multiple large registries and mechanistic studies confirm that aHUS is a thrombotic microangiopathy driven by uncontrolled activation of the alternative complement pathway, with genetic variants identified in approximately 50–60% of patients. As stated by Rojas-López et al., "Atypical hemolytic uremic syndrome (aHUS) is a rare, life-threatening thrombotic microangiopathy (TMA) characterized by complement dysregulation, leading to microvascular thrombosis and multi-organ injury" (PMID: 40217974).

The key genes and their frequencies in aHUS patients were established by Frémeaux-Bacchi et al., who documented that "different groups have demonstrated genetic predisposition to atypical HUS (aHUS) involving five genes encoding for complement components which play a role in the activation or control of the alternative pathway: encoding factor H (CFH), accounting for 30% of aHUS; CD46 (encoding membrane cofactor protein [MCP]) accounting for approximately 10% of aHUS; CFI (encoding factor I) accounting for an estimated 5-15% of patients; C3 (encoding C3) accounting for approximately 10% of aHUS; and rarely CFB (encoding factor B)" (PMID: 21376430).

The autoimmune form involving anti-factor H antibodies has been documented in 5–11% of cases: "Factor H autoantibodies (anti-FHs) have been reported in aHUS in 5-11% of cases and are strongly associated with the homozygous deletion of CFHR3-CFHR1 genes" (PMID: 35405682).

Gene	Protein	Frequency in aHUS	Function	Mutation Consequence
CFH	Complement Factor H	~30%	Fluid-phase and surface complement regulator	Loss of function
CD46/MCP	Membrane Cofactor Protein	~10%	Membrane-bound complement regulator	Loss of function
CFI	Complement Factor I	5–15%	Serine protease cleaving C3b/C4b	Loss of function
C3	Complement C3	~10%	Central complement component	Gain of function
CFB	Complement Factor B	1–4%	Alternative pathway activator	Gain of function
THBD	Thrombomodulin	~5%	Endothelial anticoagulant/complement regulator	Loss of function
DGKE	Diacylglycerol Kinase Epsilon	Rare	Lipid signaling, non-complement	Loss of function
Anti-FH Ab	(autoimmune)	5–11%	Blocks CFH surface recognition	Functional CFH deficiency

Finding 2: Incomplete Penetrance and Gene-Environment Interactions Are Fundamental to aHUS

Only approximately 50% of individuals carrying pathogenic complement variants ever develop clinical aHUS, establishing that environmental triggers are necessary to overwhelm the already-compromised complement regulatory capacity. As stated: "Despite the presence of an underlying genetic etiology, an environmental trigger is often necessary to manifest disease, a phenomenon known as incomplete penetrance. These triggers could include infections, pregnancy, medication, cancers, or ischemia-reperfusion injury" (PMID: 40670222).

This two-hit model was further established: "Predisposition to aHUS is inherited with incomplete penetrance. It is admitted that mutations confer a predisposition to develop aHUS rather than directly causing the disease and that a second event (genetic or environmental) is required for disease manifestation" (PMID: 21376430).

Data from the Global aHUS Registry (n=307 patients with identifiable triggers) quantified specific trigger frequencies: "Malignancy was most common (58/307, 18.9%), followed by pregnancy and acute infections (both 53/307, 17.3%)" (PMID: 38604995).

Finding 3: C5 Inhibitors (Eculizumab/Ravulizumab) Have Transformed aHUS Outcomes

Eculizumab (anti-C5 monoclonal antibody), approved by the FDA in 2011, and its long-acting successor ravulizumab have dramatically improved patient outcomes. In Japanese post-marketing surveillance of dialysis-dependent patients treated with eculizumab: "Of 38 included patients, 21 (55.3%) and 17 (44.7%) were placed in Groups A and B, respectively. No patient re-started dialysis" (PMID: 41148448). Earlier treatment initiation (<15 days from TMA onset) was associated with dialysis discontinuation (p=0.008).

Genotype-specific relapse risk after treatment discontinuation has been characterized: "Pathogenic gene variants in complement-regulating proteins, particularly CFH, CFI, MCP/CD46, and C3, significantly increase the risk of relapse, particularly within the first 3 to 12 months after cessation" (PMID: 41347985).

Real-world data from 60 patients switching to ravulizumab confirmed maintained effectiveness: "This is the first real-world cohort analysis of data from patients treated with ravulizumab and reinforces the real-world safety and effectiveness data of ravulizumab in patients with aHUS who switched from eculizumab" (PMID: 39291212).

Finding 4: aHUS Epidemiology — Rare Disease with Female Predominance in Adults

Belgian registry data established a population-based prevalence: "A total of 121 Belgian patients were registered in the Global aHUS Registry, resulting in a prevalence of 10.4 aHUS patients per million inhabitants, with a higher proportion of females affected (57.9% vs 42.1% of males)" (PMID: 41102576).

A striking age-dependent sex ratio reversal was documented: "A sex-specific difference was apparent according to age at initial disease onset as the ratio of males to females was 1.3:1 for childhood presentation and 1:2 for adult presentation" (PMID: 29907460). The female predominance in adults is likely attributable to pregnancy as a disease trigger.

UK Registry data quantified genotype-specific prognosis: "ESKD-free survival probability at five years was 0.80 for paediatric patients and 0.57 for adults. ESKD-free survival was negatively influenced by CFH, C3, or CFI variants" (PMID: 40764536).

Finding 5: Mouse Models Confirm the Causal Role of Complement Dysregulation in aHUS

Landmark mouse models have provided definitive in vivo proof of the complement dysregulation mechanism. The first aHUS mouse model (Cfh(−/−).FHΔ16-20) demonstrated that "these mice, transgenically expressing a mouse FH protein functionally equivalent to aHUS-associated human FH mutants, regulate C3 activation in plasma and spontaneously develop aHUS but not MPGN2. These animals represent the first model of aHUS and provide in vivo evidence that effective plasma C3 regulation and the defective control of complement activation on renal endothelium are the critical events in the molecular pathogenesis of FH-associated aHUS" (PMID: 17517971).

Critically, C5-deficient mice were completely protected: "spontaneous aHUS did not develop in any of the C5-deficient mice" (PMID: 21148255), providing the direct mechanistic rationale for therapeutic C5 inhibition with eculizumab.

The FH W1206R knock-in mouse model further showed that "disruption of FH function on the cell surface can also lead to disseminated complement-dependent macrovascular thrombosis" (PMID: 28057640), with both micro- and macrovascular thrombosis, retinal ischemia, and 48% premature mortality.

Mechanistic Model: From Genetic Predisposition to Clinical Disease

The pathogenesis of aHUS can be understood as a multi-step cascade where genetic susceptibility and environmental insults converge on the complement system:

STEP 1: GENETIC PREDISPOSITION (Upstream)
┌──────────────────────────────────────────────────────┐
│ Complement gene variant(s):                           │
│ CFH, CD46, CFI, C3, CFB, THBD, DGKE                 │
│ OR anti-FH autoantibodies                             │
│                                                       │
│ → Impaired complement regulation on endothelial       │
│   cell surfaces                                       │
│ → Normal plasma complement control preserved          │
│ → Subclinical carrier state (~50% lifetime disease    │
│   risk)                                               │
└────────────────────────┬─────────────────────────────┘
         ↓
STEP 2: ENVIRONMENTAL TRIGGER — "SECOND HIT" (Upstream)
┌──────────────────────────────────────────────────────┐
│ Infection (17.3%), pregnancy (17.3%),                 │
│ malignancy (18.9%), surgery, medications              │
│                                                       │
│ → Complement activation via innate immunity           │
│ → Direct endothelial stress/injury                    │
│ → Overwhelms compromised regulatory capacity          │
└────────────────────────┬─────────────────────────────┘
         ↓
STEP 3: COMPLEMENT AMPLIFICATION LOOP (Central)
┌──────────────────────────────────────────────────────┐
│ Uncontrolled C3b deposition on endothelium            │
│ C3 convertase (C3bBb) amplification loop              │
│ C5 convertase formation → C5a + C5b-9 (MAC)          │
│                                                       │
│ GO:0006957 (complement activation, alternative        │
│   pathway)                                            │
│                                                       │
│ ★ THERAPEUTIC TARGET: C5 inhibitors block here ★      │
└────────────────────────┬─────────────────────────────┘
         ↓
STEP 4: ENDOTHELIAL INJURY AND THROMBOSIS (Downstream)
┌──────────────────────────────────────────────────────┐
│ MAC insertion → endothelial cell damage               │
│ C5a → neutrophil recruitment, NETosis                 │
│ Loss of anticoagulant endothelial properties          │
│ Platelet adhesion and fibrin deposition               │
│                                                       │
│ → Microvascular thrombosis (TMA)                      │
│   CL:1001005 (glomerular endothelial cell)            │
│   CL:0000233 (platelet)                               │
│   CL:0000775 (neutrophil)                             │
└────────────────────────┬─────────────────────────────┘
         ↓
STEP 5: CLINICAL MANIFESTATION (Downstream)
┌──────────────────────────────────────────────────────┐
│ TMA TRIAD:                                            │
│ • Mechanical hemolysis (MAHA) — HP:0004855            │
│ • Consumptive thrombocytopenia — HP:0001873           │
│ • Organ ischemia/injury — HP:0001919 (AKI)           │
│                                                       │
│ Extrarenal: CNS (~18%), cardiac (~19%), GI (~26%)     │
│                                                       │
│ Primary organ: Kidney (UBERON:0002113)                │
│ Key structure: Renal glomerulus (UBERON:0000074)      │
└──────────────────────────────────────────────────────┘

Key molecular players and their GO annotations: - GO:0006956 — Complement activation - GO:0006957 — Complement activation, alternative pathway - GO:0030449 — Regulation of complement activation - GO:0007596 — Blood coagulation - GO:0006954 — Inflammatory response - GO:0030168 — Platelet activation

Comprehensive Disease Characterization

1. Disease Information

Overview: Atypical Hemolytic Uremic Syndrome (aHUS) is a complement-mediated thrombotic microangiopathy characterized by microvascular endothelial injury leading to thrombosis, mechanical hemolysis, consumptive thrombocytopenia, and organ damage — predominantly affecting the kidneys. Unlike typical HUS caused by Shiga toxin-producing E. coli (STEC-HUS), aHUS arises from intrinsic dysregulation of the complement system.

Database	Identifier
MONDO	MONDO:0019632
OMIM	#235400 (aHUS1/CFH); #612922 (aHUS2/CD46); #612923 (aHUS3/CFI); #612924 (aHUS4/CFB); #612925 (aHUS5/C3); #612926 (aHUS6/THBD); #615008 (aHUS7/DGKE)
Orphanet	ORPHA:2134
ICD-10	D59.3
ICD-11	3A21.1
MeSH	D065766

Synonyms: Complement-mediated TMA (CM-TMA), complement-mediated HUS, non-Shiga toxin-associated HUS, D− HUS (historical), primary aHUS.

Information sources: Aggregated from international patient registries (Global aHUS Registry), OMIM, Orphanet, GeneReviews, and 58 reviewed publications from PubMed.

2. Etiology

Primary causes: Genetic loss-of-function mutations in complement regulatory proteins (CFH, CFI, CD46, THBD) or gain-of-function mutations in complement activators (C3, CFB); acquired anti-factor H autoantibodies (5–11%); non-complement pathway via DGKE mutations (rare autosomal recessive form).

Genetic risk factors: See Finding 1 table above. A 400-patient genetic analysis additionally implicated PLG (plasminogen) as a novel aHUS gene enriched for ultrarare coding variants (PMID: 30377230). CFHR1-CFHR3 homozygous deletion is strongly associated with anti-FH autoantibodies (91.6% vs 9.8% in controls; PMID: 36622444). IgM class anti-FH autoantibodies were detected in 3.8% of patients, potentially explaining some previously "idiopathic" cases (PMID: 33712527).

Environmental triggers: Infections (respiratory, gastrointestinal, H1N1, SARS-CoV-2), pregnancy/postpartum, malignancy, medications (calcineurin inhibitors, anti-VEGF agents), organ transplantation (ischemia-reperfusion), and autoimmune disease flares. SARS-CoV-2 spike proteins directly activate the alternative complement pathway (PMID: 32877502).

Protective factors: CD46/MCP mutations associate with better prognosis. Early complement inhibitor therapy (<15 days) improves outcomes. Meningococcal vaccination is essential before C5 inhibitor therapy.

3. Phenotypes

Core clinical triad (>95% frequency each):

Phenotype	HPO Term	Severity	Progression
Microangiopathic hemolytic anemia	HP:0004855	Moderate-severe	Episodic, acute
Thrombocytopenia	HP:0001873	Moderate-severe	Episodic
Acute kidney injury	HP:0001919	Severe (40–50% require dialysis)	May progress to CKD/ESKD

Additional renal phenotypes: Proteinuria (HP:0000093; nephrotic-range in 73.3%; PMID: 41793014), hematuria (HP:0000790), hypertension (HP:0000822), chronic kidney disease (HP:0012622; 39% progress to CKD 3–4), ESKD (HP:0003774; 37% if untreated).

Extrarenal manifestations (19–38% of patients): Gastrointestinal involvement is most common (~26%; pancreatitis HP:0001733, colitis HP:0002583), followed by cardiovascular (~19%; cardiomyopathy HP:0001638), and neurological (~18%; seizures HP:0001250, stroke HP:0001297, encephalopathy).

Laboratory abnormalities: Elevated LDH (HP:0025435), low haptoglobin (decreased in 89.3%), schistocytes (HP:0001927), low C3 (HP:0005421; up to 90% in pediatric cohorts), normal ADAMTS13 activity (>10%).

Age of onset: Bimodal — mean 4.9 years (pediatric), 37.8 years (adult); overall 23.6 years (PMID: 40764536). DGKE-aHUS presents in infancy; anti-FH antibody form typically in school-age children.

4. Genetic/Molecular Information

Causal genes (HGNC IDs): CFH (HGNC:4883), CD46 (HGNC:6953), CFI (HGNC:5394), C3 (HGNC:1318), CFB (HGNC:1037), THBD (HGNC:11784), DGKE (HGNC:2852), PLG (HGNC:9071, newly implicated).

Pathogenic variants: CFH mutations predominantly cluster in SCR 19–20, impairing surface recognition while preserving plasma regulatory activity. A novel homozygous CD46 mutation c.1127+2T>A was recently identified with functional validation showing reduced mRNA/protein expression (PMID: 40983966). Variants with MAF >0.1% should not be considered pathogenic without functional evidence (PMID: 30377230). 30–40% of patients carry VUS requiring further characterization (PMID: 39644051).

Chromosomal abnormalities: The 1q31.3 CFHR gene cluster is prone to non-allelic homologous recombination producing deletions (CFHR1-CFHR3), duplications, and hybrid genes (CFH-CFHR fusions).

Modifier genes: CFHR1-5 gene copy number variants, MCP polymorphisms, and combined mutations (digenic/oligogenic inheritance) increase disease penetrance and severity.

5. Environmental Information

No specific toxins or occupational exposures are established as direct aHUS causes. Key infectious triggers include Mycoplasma pneumoniae (associated with anti-FH antibody development; PMID: 35405682), H1N1 influenza (<30 reported cases; DOI: 10.5414/CNCS111525), and SARS-CoV-2 (spike protein directly activates the alternative pathway; PMID: 32877502).

6. Mechanism / Pathophysiology

Molecular pathways: The central pathway is the alternative complement pathway (KEGG: hsa04610; Reactome: R-HSA-173736). Genetic defects impair C3b inactivation on endothelial surfaces → uncontrolled C3 convertase (C3bBb) amplification → C5 convertase formation → C5a (anaphylatoxin) + C5b-9 (MAC) generation → endothelial injury.

Protein dysfunction: CFH mutations in SCR 19–20 impair surface recognition while maintaining fluid-phase regulation — the critical distinction proven by mouse models (PMID: 17517971). CFH also has three heparin-binding sites (SCR 7, SCR 9, SCR 20) mediating endothelial surface interactions (PMID: 16263173).

Cellular processes: Endothelial activation/injury (GO:0002544), platelet activation (GO:0030168), NETosis, inflammation (GO:0006954), and MAC-mediated cell death. Complement-coagulation-neutrophil cross-talk amplifies TMA (PMID: 36642429).

Cell types involved: Glomerular endothelial cells (CL:1001005; primary target), platelets (CL:0000233), neutrophils (CL:0000775), podocytes (CL:0000653; secondary), tubular epithelial cells (CL:1000494; ischemic).

Immune involvement: Autoimmunity (anti-FH IgG and IgM autoantibodies; PMID: 33712527); complement-coagulation cross-talk; SLE-associated aHUS (PMID: 41173493).

7. Anatomical Structures Affected

Primary organ: Kidney (UBERON:0002113) — renal glomeruli (UBERON:0000074) and arterioles (UBERON:0001980) are the predominant sites of TMA.

Secondary organs: Brain (UBERON:0000955; ~18%), heart (UBERON:0000948; ~19%), GI tract (UBERON:0005409; ~26%), lung (UBERON:0002048; rare), eye (UBERON:0000970; retinal thrombosis demonstrated in FH W1206R mice; PMID: 30711487).

Subcellular: Cell membrane (GO:0005886) — MAC insertion site; extracellular space (GO:0005615) — complement cascade.

Lateralization: Bilateral kidney involvement (symmetric).

8. Temporal Development

Onset: Acute; bimodal age distribution (pediatric mean 4.9 years, adult mean 37.8 years). Onset typically follows a triggering event.

Progression: Episodic/relapsing-remitting without treatment. 57% of patients experience additional TMA events. Without treatment: ESKD-free survival at 5 years is 0.80 (pediatric) and 0.57 (adult) (PMID: 40764536). With C5 inhibitors: hematological remission ~80%, >55% discontinue dialysis.

Relapse patterns: Highest risk 3–12 months after treatment discontinuation, genotype-dependent. CFH carries highest relapse risk; CD46 carries lowest.

Critical periods: Pregnancy/postpartum, post-transplant, post-infectious episodes.

9. Inheritance and Population

Epidemiology: Prevalence ~10.4 per million (Belgian registry; PMID: 41102576)); incidence ~0.5–2 per million per year.

Inheritance: Predominantly autosomal dominant with incomplete penetrance (~50%) for CFH, CFI, C3, CFB, THBD. Autosomal recessive for DGKE and some CD46 families. Digenic/oligogenic patterns recognized.

Sex ratio: Overall 57.9% female. Male:female = 1.3:1 in childhood, 1:2 in adults (PMID: 29907460). Adult female predominance attributable to pregnancy as trigger.

Geographic distribution: Worldwide; anti-FH antibody form more prevalent in Indian subcontinent; population-specific genetic profiles documented (Brazilian: PMID: 39918340; Australian: PMID: 32378251).

10. Diagnostics

Clinical tests: CBC with smear (schistocytes), LDH, haptoglobin, Coombs test (negative), creatinine, complement levels (C3, C4, Factor H, Factor I, sC5b-9), ADAMTS13 activity (>10% excludes TTP), anti-Factor H antibodies, Shiga toxin testing (excludes STEC-HUS).

Genetic testing: Recommended for all patients — comprehensive NGS gene panel (minimum: CFH, CFI, CD46, C3, CFB, THBD, DGKE; extended: CFHR1-5, PLG) plus MLPA for structural variants. WES for novel gene discovery. Anti-FH antibody ELISA in all patients. Turnaround time: weeks — treatment should not be delayed (PMID: 39644051).

Biopsy findings: Glomerular/arteriolar TMA with endothelial swelling, fibrin-platelet thrombi, "onion-skin" intimal proliferation, mesangiolysis, cortical necrosis (severe).

Differential diagnosis: TTP (ADAMTS13 <10%), STEC-HUS (Shiga toxin+), HELLP syndrome, malignant hypertension-TMA (complement variants found in 25%; PMID: 39106497), drug-induced TMA, autoimmune disease-associated TMA, cobalamin C deficiency, G6PD deficiency (can mimic aHUS; PMID: 29248304).

Screening: Cascade genetic screening recommended for first-degree relatives. Not included in newborn screening programs.

11. Outcome/Prognosis

Pre-eculizumab era: 33–40% mortality/ESKD at first episode; 65% overall ESKD progression.

Post-eculizumab era: Hematological remission ~80%; 55.3% of dialysis patients discontinue dialysis (PMID: 41148448); post-transplant TMA: 68% graft survival at 12 months with eculizumab (PMID: 41368132).

Genotype-prognosis correlations:

Genotype	ESKD Risk	Relapse Risk	Transplant Recurrence
CFH	Highest (~60%)	High	~80%
CFI	High	Moderate	~50%
C3	Moderate-High	Moderate	~50%
CD46/MCP	Lowest (~20%)	Low-Moderate	<20%
Anti-FH Ab	Variable	High if untreated	Possible

Prognostic factors: Genotype (CFH worst, CD46 best), age at onset (childhood better), time to treatment (<15 days improves outcomes; p=0.008), presence of hypertension (less frequent in recovery group: 28.6% vs 64.7%, p=0.022), and multiple pathogenic variants (PMID: 41347985).

12. Treatment

First-line — Complement C5 inhibitors (MAXO:0001298): - Eculizumab (Soliris®): Anti-C5 monoclonal antibody; IV q2 weeks; FDA-approved 2011 - Ravulizumab (Ultomiris®): Long-acting anti-C5; IV q8 weeks; confirmed real-world effectiveness (PMID: 39291212) - Mandatory meningococcal vaccination before treatment (MenACWY + MenB)

Plasma therapy (MAXO:0000755): Historical first-line; now bridge therapy or when C5 inhibitors unavailable. Plasma exchange removes autoantibodies and mutant proteins; plasma infusion provides normal complement regulators.

Immunosuppression (anti-FH antibody form): Rituximab, mycophenolate mofetil, corticosteroids.

Emerging therapies: - Iptacopan/LNP023 (oral Factor B inhibitor): First successful use in SLE-aHUS (PMID: 40996634) - Factor D inhibitors: Block upstream complement activation (PMID: 32877502) - Anti-properdin: Prevents TMA in mouse models (PMID: 29858280)

Kidney transplantation (MAXO:0001175): For ESKD patients; requires genotype-based risk assessment and prophylactic eculizumab for high-risk genotypes.

Treatment discontinuation: Genotype-guided — CFH: generally continued indefinitely; CD46: safer to discontinue. Close monitoring mandatory for 3–12 months post-cessation.

13. Prevention

Primary prevention: Genetic counseling (MAXO:0000079) for affected families; no population-level primary prevention exists.

Secondary prevention: Cascade genetic screening of first-degree relatives; biomarker monitoring in at-risk individuals; trigger awareness education.

Tertiary prevention: Prophylactic eculizumab pre-transplant; prompt treatment at relapse signs; lifelong complement inhibition for high-risk genotypes; meningococcal vaccination (MAXO:0000759).

14. Other Species / Natural Disease

No well-documented naturally occurring aHUS in companion animals. Complement system is highly conserved across vertebrates. Orthologous genes: mouse Cfh (NCBI Gene: 12628), C3 (12266), Cfi (12630), Cfb (14962), Cd46 (17221). CFH surface recognition domain function is conserved, as demonstrated by mouse models faithfully recapitulating human disease.

15. Model Organisms

Cfh(−/−).FHΔ16-20 mice: First aHUS model; expresses truncated FH lacking surface-binding domains; spontaneous renal TMA (PMID: 17517971).

FH W1206R knock-in mice: Point mutation model; renal TMA + systemic thrombophilia + retinal ischemia; 48% premature death (PMID: 28057640; PMID: 30711487).

C5-deficient crosses: Complete protection from aHUS, proving C5 is essential (PMID: 21148255) — direct rationale for eculizumab.

Anti-properdin treated mice: Blocking properdin prevents TMA and thrombophilia (PMID: 29858280).

Model limitations: Homozygous backgrounds (humans typically heterozygous); incomplete penetrance poorly modeled in inbred strains; most models focus on CFH; drug pharmacokinetic differences limit direct translation.

Evidence Base

Key Supporting Literature

Citation	Contribution	Evidence Type
PMID: 40217974	Comprehensive aHUS review: complement dysregulation, multiorgan involvement	Clinical review
PMID: 21376430	Established gene frequencies and two-hit model	Clinical/genetic
PMID: 17517971	First mouse model proving surface complement dysregulation	Model organism
PMID: 21148255	C5 dependence of aHUS — rationale for eculizumab	Model organism
PMID: 28057640	FH W1206R mouse: systemic thrombophilia	Model organism
PMID: 29907460	Global Registry: genotype-phenotype correlations (n=851)	Clinical registry
PMID: 30377230	400-patient genetic analysis; PLG as new gene	Genetic study
PMID: 41102576	Belgian registry: prevalence 10.4/million	Population epidemiology
PMID: 40764536	UK registry: ESKD-free survival, genotype-prognosis	Clinical registry
PMID: 38604995	Trigger characterization (n=307)	Clinical registry
PMID: 41148448	Eculizumab: 55.3% dialysis discontinuation	Post-marketing surveillance
PMID: 39291212	Ravulizumab real-world effectiveness	Clinical registry
PMID: 41347985	Genotype-specific relapse risk	Clinical review
PMID: 40670222	Gene-environment interaction framework	Mechanistic review
PMID: 35405682	Anti-FH antibodies: 5–11% prevalence	Clinical study
PMID: 36622444	Complement variants in anti-FH aHUS: 3% pathogenic	Meta-analysis
PMID: 39644051	Diagnosis, management, discontinuation consensus	Clinical guideline
PMID: 40983966	Novel CD46 mutation c.1127+2T>A	Genetic/functional
PMID: 40996634	First iptacopan use in SLE-aHUS	Case report
PMID: 32877502	SARS-CoV-2 spike activates alternative pathway	In vitro

Limitations and Knowledge Gaps

Genetically unresolved cases (30–40%): Despite comprehensive testing, no pathogenic variant is identified in a substantial proportion of patients. Additional genetic, epigenetic, and environmental factors remain to be discovered.
VUS interpretation: 30–40% of identified variants are classified as VUS. Functional validation assays are not standardized or widely available (PMID: 39644051).
Treatment discontinuation criteria: While genotype-guided approaches are emerging, precise biomarkers to predict safe discontinuation are lacking. The optimal duration of C5 inhibitor therapy remains undefined for many genotypes.
Upstream complement inhibition: C5 inhibitors leave upstream C3 activation unchecked. Whether proximal complement inhibitors (Factor B, Factor D, C3) offer superior outcomes remains under investigation.
Registry biases: Most data derive from developed nations with access to eculizumab. Global epidemiology in low-resource settings is poorly characterized. The Brazilian case report (PMID: 41425686) illustrates how limited access impacts outcomes.
Epigenetic contributions: Virtually no data on epigenetic modifications in aHUS pathogenesis.
Quality of life data: Formal QoL studies using validated instruments specific to aHUS are limited.
Long-term outcomes: With complement inhibitors available only since 2011, truly long-term (>15 year) outcome data are still maturing.
Pregnancy management: Optimal management of pregnancy in women with known complement variants remains poorly defined.
Non-complement aHUS: The role of DGKE and other non-complement pathways is incompletely understood.

Proposed Follow-up Research and Actions

High Priority

Functional characterization of VUS: Develop standardized high-throughput assays (hemolytic assays, surface protection assays) for complement gene variants to reclassify the 30–40% of patients with VUS.
Biomarker development for treatment discontinuation: Prospective studies correlating complement biomarkers (sC5b-9, C3d, Bb) with relapse risk to enable personalized treatment duration decisions.
Clinical trials of proximal complement inhibitors: Head-to-head trials comparing Factor B inhibitors (iptacopan), Factor D inhibitors, and C3 inhibitors against C5 inhibitors.

Moderate Priority

Whole-genome sequencing studies: To identify non-coding regulatory variants, structural variants, and novel genes in genetically unresolved aHUS.
Single-cell transcriptomics of aHUS renal biopsies: Characterize endothelial cell subtypes and immune cell populations at single-cell resolution.
Epigenome-wide association studies: Investigate DNA methylation patterns in complement regulatory genes and their association with disease penetrance.
Global epidemiology studies: Characterize population-specific genetics and outcomes in under-represented populations.

Lower Priority

Additional animal models: CFI, C3, and CD46 mutation mouse models for genotype-specific pathophysiology.
Long-term outcome registries: 20+ year follow-up of patients on complement inhibitors.
AI-based variant interpretation: Machine learning models trained on functional data to predict pathogenicity of novel complement variants.

Ontology Term Summary

Category	Terms
MONDO	MONDO:0019632 (atypical hemolytic uremic syndrome)
HPO	HP:0004855 (MAHA), HP:0001873 (thrombocytopenia), HP:0001919 (AKI), HP:0000093 (proteinuria), HP:0000822 (hypertension), HP:0001927 (schistocytosis), HP:0025435 (elevated LDH), HP:0005421 (low C3), HP:0001250 (seizures), HP:0001638 (cardiomyopathy), HP:0012622 (CKD), HP:0001733 (pancreatitis)
GO (BP)	GO:0006956 (complement activation), GO:0006957 (alternative pathway), GO:0030449 (regulation of complement), GO:0007596 (coagulation), GO:0006954 (inflammation), GO:0030168 (platelet activation)
GO (CC)	GO:0005886 (plasma membrane), GO:0005615 (extracellular space)
CL	CL:1001005 (glomerular endothelial cell), CL:0000233 (platelet), CL:0000775 (neutrophil), CL:0000653 (podocyte), CL:1000494 (renal tubular epithelial cell)
UBERON	UBERON:0002113 (kidney), UBERON:0000074 (renal glomerulus), UBERON:0000955 (brain), UBERON:0000948 (heart), UBERON:0005409 (GI tract), UBERON:0002048 (lung)
CHEBI	CHEBI:149504 (eculizumab), CHEBI:190524 (ravulizumab)
MAXO	MAXO:0001298 (complement inhibitor therapy), MAXO:0000602 (dialysis), MAXO:0001175 (kidney transplantation), MAXO:0000755 (plasma exchange), MAXO:0000759 (vaccination), MAXO:0000079 (genetic counseling)

Report generated from systematic review of 58 publications, international registry data, and mechanistic studies. All claims are supported by cited primary literature with PMIDs. Evidence types include human clinical data (registries, case series, meta-analyses), model organism studies (mouse genetic models), in vitro functional assays, and computational analyses.

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Subtypes

Pathophysiology

Pathograph

Phenotypes

Genetic Associations

Treatments

Environmental Factors

Biochemical Markers

Source YAML

References & Deep Research

References

Deep Research

1. Disease Information (concise overview; current understanding)

2. Etiology

2.1 Disease causal factors

2.2 Risk factors (genetic; triggers as “environmental/clinical exposures”)

2.3 Protective factors

2.4 Gene–environment interaction

3. Phenotypes (clinical, laboratory, QoL)

3.1 Core phenotype (TMA triad)

3.2 Renal phenotype (primary)

3.3 Extrarenal manifestations (selected; with frequencies where available)

3.4 Quality of life (QoL) impact

3.5 Suggested HPO terms (examples; not exhaustive)

4. Genetic / Molecular Information

4.1 Causal genes (core set supported in retrieved evidence)

4.2 Variant types / functional consequences (high-level)

4.3 Gene-level frequency estimates (from review excerpts)

4.4 Anti–factor H autoantibodies and CFHR deletions

4.5 Modifier genes / oligogenicity

4.6 Penetrance and expressivity

4.7 Epigenetic information / chromosomal abnormalities

5. Environmental Information (triggers and exposures)

6. Mechanism / Pathophysiology

6.1 Causal chain (current consensus)

6.2 Cellular and tissue targets

6.3 Biomarkers / functional assays (recent developments)

7. Anatomical Structures Affected

7.1 Organ level (UBERON suggestions)

7.2 Tissue and cell level

7.3 Subcellular level

8. Temporal Development

8.1 Onset

8.2 Progression

8.3 Relapse/recurrence

9. Inheritance and Population

9.1 Epidemiology (statistics)

9.2 Inheritance pattern

9.3 Population demographics

10. Diagnostics

10.1 Clinical tests and biomarkers

10.2 Differential diagnosis (must exclude)

10.3 Complement testing (caveats)

10.4 Genetic testing strategy

11. Outcome / Prognosis

11.1 Renal outcomes

11.2 Pregnancy-associated aHUS (p-aHUS) outcomes (systematic review/meta-analysis; 2025, searches through Mar 2024)

12. Treatment

12.1 Pharmacotherapy (current standard; real-world implementation)

12.2 Supportive care / plasma exchange

12.3 Prevention / prophylaxis related to therapy

12.4 Suggested MAXO terms (examples)

13. Prevention

14. Other Species / Natural Disease

15. Model Organisms

Recent developments and 2023–2024 highlights (prioritized)

Summary statistics and key points table

Limitations of this evidence package

Key Findings

Finding 1: aHUS Is Caused by Dysregulation of the Alternative Complement Pathway

Finding 2: Incomplete Penetrance and Gene-Environment Interactions Are Fundamental to aHUS

Finding 3: C5 Inhibitors (Eculizumab/Ravulizumab) Have Transformed aHUS Outcomes

Finding 4: aHUS Epidemiology — Rare Disease with Female Predominance in Adults

Finding 5: Mouse Models Confirm the Causal Role of Complement Dysregulation in aHUS

Mechanistic Model: From Genetic Predisposition to Clinical Disease

Comprehensive Disease Characterization

1. Disease Information

2. Etiology