IgA Nephropathy

IgA Nephropathy (IgAN), also known as Berger's disease, is the most common primary glomerulonephritis worldwide. It is defined by a defect in IgA1 O-glycosylation that produces galactose-deficient IgA1 (Gd-IgA1), which triggers autoantibody formation, circulating immune complex deposition in the glomerular mesangium, complement activation, and progressive kidney injury. The disease affects people of all ages but peaks in the second and third decades of life, and up to 50% of high-risk patients develop end-stage renal disease within 20–25 years.

Table of Contents

  1. Overview
  2. Epidemiology
  3. Pathophysiology
  4. Clinical Presentation
  5. MEST-C Oxford Classification
  6. Diagnosis
  7. Treatment
  8. Prognosis and Progression to ESRD
  9. Recent Clinical Trials
  10. Prevention and Monitoring
  11. Research Papers (PubMed searches)
  12. References
  13. Featured Videos

1. Overview

IgA Nephropathy (IgAN), also known as Berger's disease (after Jean Berger who first described it in 1968), is the most common primary glomerulonephritis worldwide, accounting for 30–40% of primary GN in developed countries. The disease is characterized by predominant IgA1 immune deposits in the glomerular mesangium, leading to mesangial cell proliferation, complement activation, and progressive kidney injury. IgAN affects people of all ages but peaks in the second and third decades of life with a 2:1 male predominance. Though often considered a mild condition, up to 50% of high-risk patients develop end-stage renal disease (ESRD) within 20–25 years.

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2. Epidemiology

IgAN exhibits marked geographic variation, with the highest prevalence in Asia (particularly Japan and China, where it accounts for up to 40–50% of primary GN biopsies) and lower prevalence in Black populations. Annual incidence is approximately 2.5 cases per 100,000 in Western countries. The disease accounts for approximately 10% of patients on dialysis in developed nations. Family clustering occurs in 5–10% of cases, suggesting genetic susceptibility involving HLA loci (HLA-DR4, HLA-B35) and genes regulating galactose-deficient IgA1 production.

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3. Pathophysiology

The multi-hit hypothesis for IgAN pathogenesis involves four sequential steps:

Hit 1 — Elevated circulating galactose-deficient IgA1 (Gd-IgA1): O-glycan chains on the hinge region of IgA1 are underglycosylated due to reduced activity of the enzyme C1GALT1 and its chaperone COSMC, leading to exposure of N-acetylgalactosamine (GalNAc) residues. Elevated Gd-IgA1 is found in patients and their first-degree relatives.

Hit 2 — Autoantibody formation: Gd-IgA1 is recognized as a neoantigen, triggering production of IgG and IgA autoantibodies directed against the abnormal hinge-region glycans.

Hit 3 — Immune complex formation: Autoantibodies bind Gd-IgA1, forming large immune complexes with high mesangial affinity.

Hit 4 — Mesangial injury: Immune complex deposition in the mesangium activates the lectin pathway of complement (C4d deposition) and the alternative pathway, triggering mesangial cell proliferation, cytokine release (TGF-β, PDGF, IL-6), and eventual glomerulosclerosis and tubular atrophy.

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4. Clinical Presentation

Three classic presentations:

Synpharyngitic gross hematuria: Episodic gross hematuria occurring within 24–72 hours of a mucosal infection (typically upper respiratory tract infection), distinguishing IgAN from post-streptococcal GN (which has a 2–3 week latency). Tea-colored or brown urine with flank pain. Common in younger patients (30–40% of presentations in Asian populations).

Asymptomatic microscopic hematuria ± proteinuria: Detected incidentally on routine urinalysis. Most common presentation in Western populations (50–60%). May have low-grade proteinuria.

Chronic GN with nephrotic-range proteinuria: Hypertension, progressive CKD, proteinuria >1 g/day. Associated with the worst prognosis. Rare presentation as nephrotic syndrome proper.

Rare presentations include rapidly progressive GN (crescentic IgAN) with rapid GFR decline, and macroscopic hematuria causing AKI from tubular obstruction by RBC casts.

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5. MEST-C Oxford Classification

The Oxford Classification (2009, revised 2017) provides a standardized histological scoring system predicting renal outcomes independently of clinical parameters:

M — Mesangial hypercellularity: M0 = ≤50% of glomeruli with mesangial hypercellularity; M1 = >50%. M1 predicts faster GFR decline.

E — Endocapillary hypercellularity: E0 = absent; E1 = present in any glomerulus. E1 predicts increased risk of progression especially without immunosuppression.

S — Segmental glomerulosclerosis: S0 = absent; S1 = present (any segmental sclerosis, adhesion, or tip lesion). S1 independently predicts GFR decline and ESRD.

T — Tubular atrophy/interstitial fibrosis: T0 = 0–25%; T1 = 26–50%; T2 = >50% of cortical area. T-score is the strongest predictor of ESRD. T2 carries very high risk of progression to ESRD.

C — Crescents (added 2017): C0 = no crescents; C1 = crescents in <25% of glomeruli; C2 = crescents in ≥25%. C2 predicts poor outcomes and may indicate need for immunosuppression.

The MEST-C score supplements clinical risk factors including proteinuria, eGFR, and hypertension in predicting long-term renal outcomes.

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6. Diagnosis

Definitive diagnosis requires kidney biopsy with immunofluorescence showing dominant or codominant IgA deposits in the mesangium (IgG and IgM may be present in smaller amounts). Light microscopy shows mesangial proliferative GN. Electron microscopy confirms mesangial electron-dense deposits.

Laboratory workup:

Indications for biopsy: unexplained persistent microscopic hematuria with proteinuria >0.5 g/day, progressive CKD, or suspected rapidly progressive GN.

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7. Treatment

Supportive Therapy (all patients)

ACEi or ARB: First-line for proteinuria >0.5 g/day and/or hypertension. Target proteinuria <0.5–1 g/day. Maximize dose to tolerated level. Combined ACEi + ARB not recommended due to AKI and hyperkalemia risk.

SGLT2 inhibitors (dapagliflozin, empagliflozin): DAPA-CKD and EMPA-KIDNEY trials demonstrated kidney-protective effects in CKD including IgAN; reduce proteinuria and slow GFR decline. Now recommended by KDIGO 2021 for patients with eGFR ≥20 and proteinuria despite RAAS blockade.

Fish oil (omega-3 fatty acids): Phase III trials (FISH-IgAN) show modest and inconsistent proteinuria reduction; weak evidence. KDIGO 2021 suggests it may be used in persistent proteinuria >1 g/day despite ACEi/ARB.

Sodium bicarbonate: In patients with metabolic acidosis and CKD, bicarbonate supplementation may slow CKD progression.

Immunosuppression (selected high-risk patients)

STOP-IgAN trial (2015): Showed no benefit from adding immunosuppression to comprehensive supportive care in most patients; reinforced the importance of maximized supportive therapy first.

TESTING trial (2017/2022 extension): High-dose oral methylprednisolone (0.6–0.8 mg/kg/day × 2 months, tapered to 12 months) reduced proteinuria and ESRD risk but increased serious adverse events (infections, weight gain, diabetes). Revised low-dose protocol showed better safety profile.

NEFECON (Targeted-release budesonide): Budesonide formulated to release in the ileum (Peyer's patches — the site of mucosal IgA production). NEFIGAN Phase 2b trial (2017) and NefIgArd Phase 3 trial (2023) showed significant proteinuria reduction (−27%) and eGFR preservation with low systemic corticosteroid side effects. FDA approved as Tarpeyo in 2023.

Sparsentan: Dual endothelin/angiotensin receptor antagonist. PROTECT trial (2023) demonstrated proteinuria reduction and eGFR preservation superior to losartan alone. FDA approved 2023 for IgAN.

Atrasentan: Selective endothelin-A receptor antagonist. ALIGN Phase 3 trial ongoing; Phase 2 showed 40% proteinuria reduction.

Other agents under investigation: iptacopan (complement factor B inhibitor), cemdisiran/avacopan (complement pathway), obinutuzumab, and anti-APRIL antibodies (BION-1301) targeting the B-cell survival factor APRIL that drives Gd-IgA1 production.

Cytotoxic immunosuppression (cyclophosphamide, MMF): reserved for crescentic IgAN or rapidly progressive disease.

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8. Prognosis and Progression to ESRD

High-risk features predicting ESRD: proteinuria persistently >1 g/day, hypertension, reduced eGFR at presentation, T2 tubular atrophy/fibrosis on biopsy, crescents (C2), S1 score. Approximately 15–20% of patients reach ESRD within 10 years, 25–50% within 20–25 years.

Low-risk features: isolated microscopic hematuria without proteinuria, normal eGFR, M0E0S0T0C0 biopsy, episodic gross hematuria pattern only.

IgAN recurs in 30–60% of kidney transplants (higher rate than other GN), though graft loss from recurrence is uncommon (<10% at 10 years).

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9. Recent Clinical Trials

STOP-IgAN (Rauen et al., NEJM 2015): No benefit from adding immunosuppression to optimized supportive care; reinforced ACEi/ARB + risk factor control as primary management.

TESTING (Zhang et al., JAMA 2022): Low-dose methylprednisolone protocol reduced kidney failure risk by 50% vs. placebo (HR 0.53) with acceptable safety profile; NNT = 8 over 5 years.

NefIgArd / NEFECON (Barratt et al., Lancet 2023): Targeted-release budesonide 16 mg/day × 9 months: proteinuria reduction −27.1% vs. placebo; eGFR decline rate −1.97 mL/min/1.73m² slower; FDA-approved as Tarpeyo.

PROTECT (Heerspink et al., NEJM 2023): Sparsentan 400 mg/day vs. irbesartan: 40% greater proteinuria reduction at 36 weeks; eGFR slope preservation at 110 weeks; FDA-approved.

DAPA-CKD (Heerspink et al., NEJM 2020): Dapagliflozin reduced composite of ≥50% eGFR decline, ESRD, or renal/CV death by 39% in CKD patients; subgroup including IgAN patients showed consistent benefit.

EMPA-KIDNEY (EMPA-KIDNEY Collaborative Group, NEJM 2023): Empagliflozin reduced kidney disease progression or CV death by 28% across broad CKD population including IgAN.

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10. Prevention and Monitoring

No proven primary prevention. Tonsillectomy is practiced in Japan to reduce synpharyngitic hematuria episodes and may reduce proteinuria in selected patients (evidence limited to Asian cohorts; not recommended in Western guidelines). Avoid NSAIDs and nephrotoxins.

Annual monitoring of eGFR, urine PCR, and blood pressure in all IgAN patients. More frequent monitoring every 3–6 months for high-risk patients. Vaccination: influenza and pneumococcal vaccines are recommended given infection triggers.

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11. Research Papers (PubMed searches)

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12. References

  1. Wyatt RJ, Julian BA. IgA nephropathy. N Engl J Med. 2013;368(25):2402–2414. PMID: 23782179. https://doi.org/10.1056/NEJMra1206793
  2. Barratt J, et al. Randomized Phase 3 Trial of a Targeted-Release Formulation of Budesonide for IgA Nephropathy (NefIgArd). Lancet. 2023;401(10381):1029–1040. PMID: 36906109. https://doi.org/10.1016/S0140-6736(23)00569-4
  3. Rauen T, et al. Intensive Supportive Care plus Immunosuppression in IgA Nephropathy (STOP-IgAN). N Engl J Med. 2015;373(23):2225–2236. PMID: 26630142. https://doi.org/10.1056/NEJMoa1415463
  4. Zhang H, et al. Efficacy and Safety of Low-dose Methylprednisolone in IgA Nephropathy (TESTING). JAMA. 2022;327(19):1888–1898. PMID: 35579640. https://doi.org/10.1001/jama.2022.5368
  5. Heerspink HJL, et al. Sparsentan in Patients with IgA Nephropathy (PROTECT). N Engl J Med. 2023;389(21):1925–1935. PMID: 37889517. https://doi.org/10.1056/NEJMoa2305208
  6. Roberts ISD, et al. The Oxford classification of IgA nephropathy: pathology definitions, correlations, and reproducibility. Kidney Int. 2009;76(5):546–556. PMID: 19571790. https://doi.org/10.1038/ki.2009.168
  7. Trimarchi H, et al. Oxford Classification of IgA nephropathy 2016: an updated proposal. Kidney Int. 2017;91(5):1014–1021. PMID: 28341274. https://doi.org/10.1016/j.kint.2017.02.003
  8. Heerspink HJL, et al. Dapagliflozin in Patients with Chronic Kidney Disease (DAPA-CKD). N Engl J Med. 2020;383(15):1436–1446. PMID: 32970396. https://doi.org/10.1056/NEJMoa2024816
  9. Fellström BC, et al. Targeted-release budesonide versus placebo in patients with IgA nephropathy (NEFIGAN). Lancet. 2017;389(10084):2117–2127. PMID: 28363480. https://doi.org/10.1016/S0140-6736(17)30550-0
  10. EMPA-KIDNEY Collaborative Group. Empagliflozin in Patients with Chronic Kidney Disease. N Engl J Med. 2023;388(2):117–127. PMID: 36331190. https://doi.org/10.1056/NEJMoa2204233
  11. Mestecky J, et al. IgA nephropathy: molecular mechanisms of the disease. Annu Rev Pathol. 2013;8:217–240. PMID: 23092215. https://doi.org/10.1146/annurev-pathol-020712-163816
  12. Rajasekaran A, Julian BA, Rizk DV. IgA Nephropathy: An Interesting Autoimmune Kidney Disease. Am J Med Sci. 2021;361(2):176–194. PMID: 33041031. https://doi.org/10.1016/j.amjms.2020.10.003

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