# IgA Nephropathy

## Learning Objectives

1.  Explain the **four-hit pathogenesis model** of IgA nephropathy and identify therapeutic targets at each stage
2.  Recognize key clinical presentations and diagnostic features
3.  Compare and contrast current therapeutic options including mechanisms, efficacy, and safety profiles
4.  Develop appropriate treatment plans using evidence-based therapeutic approaches
5.  Understand emerging therapies and their potential impact on patient care
6.  Apply clinical reasoning to patient scenarios involving IgA nephropathy management

## Understanding IgA Nephropathy: The Fundamentals

IgA nephropathy represents the **most common primary kidney disease worldwide**, though its prevalence varies significantly by geography and ethnicity. The disease predominantly affects young adults, with men more commonly affected than women in a 2:1 ratio.

The hallmark is deposition of IgA-containing immune complexes in the glomerular mesangium. These deposits trigger inflammatory cascades that can lead to progressive kidney scarring and eventual kidney failure in approximately 30–40% of patients over 20 years.

## The Four-Hit Pathogenesis Model

#### Hit 1: Abnormal Antibody Production

Begins in gut-associated lymphoid tissue (Peyer's patches). Environmental triggers, genetic factors, or infections stimulate production of **galactose-deficient IgA1** antibodies lacking important sugar modifications for proper clearance.

#### Hit 2: Autoimmune Response

The immune system recognizes abnormal IgA as foreign, producing **anti-glycan autoantibodies** that specifically target the galactose-deficient regions. Creates an autoimmune response against the body's own antibodies.

#### Hit 3: Immune Complex Formation

Abnormal IgA + autoantibodies form **circulating immune complexes** with altered size and charge properties that increase their likelihood of depositing in kidneys.

#### Hit 4: Kidney Deposition & Inflammation

Immune complexes deposit in glomerular mesangium, activating **complement pathways**, triggering inflammatory cell infiltration, and stimulating fibroblast proliferation leading to progressive scarring.

## Clinical Presentation Patterns

| Pattern | Frequency | Description |
|----|----|----|
| **Classic (synpharyngitic hematuria)** | 40% | Gross hematuria within 1–3 days of respiratory infection; "tea-colored" urine |
| **Asymptomatic urinary abnormalities** | 30% | Microscopic hematuria and proteinuria discovered incidentally |
| **Nephrotic/Nephritic syndrome** | 20% | Proteinuria \>3.5 g/day, hypoalbuminemia, edema, hypertension |
| **Acute kidney injury** | 10% | Rapid GFR decline, often with crescentic GN on biopsy |

**📚 Clinical Pearl:** The classic "synpharyngitic" hematuria of IgAN occurs within 1–3 days of URI onset — this is in contrast to post-streptococcal GN where hematuria occurs 1–3 *weeks* after infection. The timing difference reflects immune complex formation (IgAN = preformed complexes activated by infection) vs. de novo immune response (PSGN).

## Diagnostic Approach and Risk Stratification

### Essential Diagnostic Studies

- **Urinalysis with microscopy:** Dysmorphic RBCs, RBC casts suggest glomerular origin
- **Serum studies:** CMP, complement levels (C3, C4 normal in IgAN), ANA, hepatitis B/C serologies
- **Kidney biopsy:** Mesangial IgA deposits on IF; Oxford Classification (MEST-C) for grading

### Risk Stratification for Treatment Planning

| Risk Level | Proteinuria | Recommended Approach | Monitoring |
|----|----|----|----|
| **Low Risk** | \<1 g/day | ACE-I/ARB optimization | Annual assessment |
| **Moderate Risk** | 1–3 g/day | TARPEYO + ACE-I/ARB | 3–6 month intervals |
| **High Risk** | \>3 g/day | Sparsentan or combination | Monthly initially |
| **Very High Risk** | \>5 g/day + declining eGFR | Combination therapy + specialist referral | Weekly initially |

## Current Treatment Arsenal

### Foundation: RAS Blockade

All patients should receive optimized RAS inhibition unless contraindicated. Maximize ACE-I or ARB dosing to the highest tolerated level. Target BP \<130/80 mmHg per the 2025 AHA/ACC guideline and the ADA Standards of Care.

KDIGO 2021 (Blood Pressure in CKD) suggests a target systolic \<120 mmHg when tolerated, using standardized office measurement (grade 2B, driven by the CKD subgroup of SPRINT). It explicitly excludes kidney transplant recipients and patients on dialysis. Much of the gap between the two numbers is measurement technique rather than disagreement about physiology: KDIGO's lower number presumes a standardized or unattended reading, which most routine clinic cuffs do not meet.

### TARPEYO (Targeted-Release Budesonide)

- **Mechanism:** Delivers budesonide specifically to Peyer's patches, targeting abnormal IgA production site
- **Evidence:** NefIgArd trial: 27% proteinuria reduction at 9 months; 50% reduction in eGFR decline rate over 2 years
- **Best for:** Moderate-risk patients (proteinuria 1–3 g/day)
- **Side effects:** Peripheral edema (17%), hypertension (12%); notably lacks serious systemic steroid complications

### Sparsentan (FILSPARI)

- **Mechanism:** First-in-class dual endothelin A receptor + angiotensin II type 1 receptor antagonist
- **Evidence:** PROTECT trial: 49.8% proteinuria reduction vs 15.1% with max-dose irbesartan; 2-year eGFR benefit of 1.2 mL/min/1.73m²/year
- **Best for:** High-risk patients (proteinuria \>1 g/day)
- **Notes:** Requires liver function monitoring (REMS). Contraindicated in pregnancy.

### Iptacopan (FABHALTA)

- **Mechanism:** Selective factor B inhibitor blocking alternative complement pathway
- **Evidence:** APPLAUSE-IgAN: 38.3% proteinuria reduction at 9 months (NNT = 14)
- **Notes:** Requires meningococcal vaccination. REMS program. Continued approval pending eGFR data.

**📚 Clinical Pearl:** Maximize ACE-I or ARB dosing to the highest tolerated level, monitoring for hyperkalemia and acute kidney function decline. This is the foundation before adding disease-specific agents. A patient on submaximal RAS blockade should not be escalated to TARPEYO or sparsentan until ACE-I/ARB is maximized.

## Emerging Therapies: The Future

### APRIL Inhibitors: Targeting the Root Cause

**Sibeprenlimab:** Phase 3 VISIONARY trial showed **51.2% proteinuria reduction** with excellent safety. Subcutaneous administration every 4 weeks. Represents the highest efficacy demonstrated for any IgAN therapy with disease-modifying potential.

### Combination Strategies

- APRIL inhibitor + complement inhibitor (upstream + downstream targeting)
- Endothelin receptor antagonist + SGLT2 inhibitor (anti-fibrotic + renoprotective)
- Triple therapy approaches for very high-risk patients
- Future: biomarker-guided combination selection based on individual pathway activation

## Case-Based Learning

#### Case 1: Moderate-Risk Patient

**Presentation:** 28-year-old with 2.4 g/day proteinuria, eGFR 85, moderate histologic changes.

**Treatment:** TARPEYO after optimizing ACE-I therapy. Result: 35% proteinuria reduction at 9 months, stable kidney function.

**Key lesson:** Risk stratification guides treatment intensity; sequential therapy allows escalation if needed.

#### Case 2: High-Risk Aggressive Disease

**Presentation:** 35-year-old male, 4.2 g/day proteinuria, eGFR decline 90 to 65 over 6 months, crescentic lesions.

**Treatment:** Sparsentan initiated with plans for combination therapy if inadequate response.

**Key lesson:** Rapidly progressive disease requires immediate intensive intervention with highest-efficacy agent.

#### Case 3: Pregnancy Planning

**Scenario:** 26-year-old female with stable IgAN planning pregnancy.

**Key lesson:** Most novel therapies are contraindicated in pregnancy. Optimize supportive care with pregnancy-compatible agents; close obstetric-nephrology collaboration essential.

## Self-Assessment Questions

**Q1:** 25-year-old female with IgAN and 2.8 g/day proteinuria is planning pregnancy in 6 months. Which approach is most appropriate?

A\) Start sparsentan  B) Initiate TARPEYO  C) Stop ACE-I once pregnant; plan pregnancy-compatible management  D) Begin combination therapy

**Answer: C** — Pregnancy planning requires compatible agents; most novel therapies are contraindicated.

**Q2:** Which mechanism best explains sparsentan's superior efficacy compared to standard ACE-I therapy?

A\) More potent angiotensin receptor blockade  B) Dual pathway targeting with synergistic effects  C) Selective complement inhibition  D) Direct anti-inflammatory properties

**Answer: B** — Dual endothelin and angiotensin receptor blockade provides synergistic benefits.

**Q3:** A patient on iptacopan develops recurrent bacterial infections. Most likely explanation?

A\) Drug intolerance  B) Complement inhibition increasing infection risk; enhance monitoring and vaccination  C) Unrelated coincidence  D) Indication for combination with antibiotics

**Answer: B** — Complement inhibition increases infection risk requiring enhanced surveillance.

## Summary: Transforming Patient Care

IgA nephropathy therapy has transformed from supportive care to targeted intervention addressing specific disease mechanisms. This represents one of the most significant advances in nephrology over the past decade.

- **Paradigm shift:** From empirical immunosuppression to mechanistically targeted interventions
- **Four-hit model:** Each hit represents a distinct intervention opportunity
- **Risk-benefit assessment:** Balancing efficacy against safety, patient preferences, and individual risk factors
- **Robust pipeline:** APRIL inhibitors, combination strategies, and biomarker-guided therapy on the horizon

## Additional Learning Resources

- KDIGO 2021 Clinical Practice Guideline for IgA Nephropathy
- PROTECT, ALIGN, APPLAUSE-IgAN trial publications
- IgA nephropathy risk prediction calculators
- Oxford Classification (MEST-C) scoring systems

## References

1.  Rodrigues JC, Haas M, Reich HN. IgA nephropathy. *CJASN*. 2017;12(4):677-686. [PubMed](https://pubmed.ncbi.nlm.nih.gov/28159829/)
2.  KDIGO 2021 Clinical Practice Guideline for the Management of Glomerular Diseases. *Kidney Int*. 2021;100(4S):S1-S276. [DOI](https://doi.org/10.1016/j.kint.2021.05.021)
3.  Barratt J, et al. Results from part A of the multi-center, double-blind, randomized, placebo-controlled NefIgArd trial (TARPEYO). *Kidney Int*. 2023;103(2):391-402. [PubMed](https://pubmed.ncbi.nlm.nih.gov/36270561/)
4.  Heerspink HJL, et al. Sparsentan in patients with IgA nephropathy (PROTECT). *Lancet*. 2023;401(10388):1584-1594. [PubMed](https://pubmed.ncbi.nlm.nih.gov/37015244/)
5.  Perkovic V, Barratt J, Rovin B, et al. Alternative Complement Pathway Inhibition with Iptacopan in IgA Nephropathy. N Engl J Med. 2025;392(6):531-543. [PubMed](https://pubmed.ncbi.nlm.nih.gov/39453772/)
6.  Trimarchi H, et al. Oxford Classification of IgA nephropathy 2016 update. *Kidney Int*. 2017;91(1):1-11. [PubMed](https://pubmed.ncbi.nlm.nih.gov/28341274/)
7.  Suzuki H, et al. The pathophysiology of IgA nephropathy. *JASN*. 2011;22(10):1795-1803. [PubMed](https://pubmed.ncbi.nlm.nih.gov/21949093/)

© Urine Nephrology Now — Clinical Mastery Series

### Also on this topic

The same subject at other levels of depth.

- **Patient handout:** [IgA Nephropathy: A Patient's Guide](https://urinenephrology.org/patient-handouts/iga-nephropathy.html)


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