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Diagnosis: C1q nephropathy

C1q nephropathy, first described by Jennette and Hipp in 1985 (Am J Kidney Dis 19856:103 [PubMed link]), is a pattern of glomerulonephritis characterized by predominant mesangial C1q deposition but with other histological features resembling lupus nephritis, although no extrarenal disease. C1q nephropathy is a poorly understood and controversial entity with distinctive immunopathologic features: dominant or co-dominant immunofluorescence staining for C1q, mesangial electron dense deposits, and no clinical or serologic evidence of systemic lupus erythematosus (SLE) (Markowitz GS et al. Kidney Int. 2003;64:1232 [PubMed link]). It is characterized clinically by heavy proteinuria or nephrotic syndrome and resistance to steroids. Up to 40% of patients have hematuria. The majority of patients are young (from <1 year to >30 years), with a median age in the teens. C1q nephropathy does not appear to be associated to extrarrenal disease.

Most C1q nephropathy patients had focal segmental glomerulosclerosis (FSGS) or minimal change disease (MCD), the majority of them presenting with corticosteroid-dependent or corticosteroid-resistant nephrotic syndrome. Many show a very poor response to immunosuppressive therapy and high risk for progressive renal insufficiency (Kersnik Levart T, et al. Pediatr Nephrol. 2005;20:1756 [PubMed link]).

Many cases of C1q nephropathy have been described as "seronegative lupus nephritis" in patients with renal histology typical of lupus nephritis who have no clinical or serological evidence of SLE. Many had histological features typical of lupus nephritis with "wire loop" appearances on light microscopy, "full house" immunoglobulin and complement deposition by immunoperoxidase, and electron-dense deposits in at least two glomerular locations (Sharman A, et al. Nephrol Dial Transplant 2004;19:1420 [PubMed link] [Free full text]).

Several morphological patterns ranging from very subtle glomerular alterations to FSGS and mesangial proliferative changes have been described. Markowitz et al (Kidney Int. 2003;64:1232 [PubMed link]) described this nephropaty as "a variant of focal segmental glomerulosclerosis", and they stated that "C1q nephropathy falls within the clinical-pathologic spectrum of MCD/FSGS". Tubules and interstitium show no abnormalities other than resorption droplets. In some cases, frequently those with FSGS, atrophic tubules and fibrosis may be present, and this feature have pronostic implicationes (chronic renal damage).

Staining for C1q is present in all glomeruli and it is intense; staining is predominantly mesangial, altough scattered capillary wall deposits may be seen in a few glomeruli in some cases. Virtually all described cases have staining for IgG, and many cases IgM and C3. IgA is frequently present. In our case only C1q is present and this feature is very inusual in the literature; we do not have a precise explanation for it, but the intense and difuse C1q deposition precludes MCD or FSGS disease, at least as usually found.

There is as yet little evidence that the defining feature of C1q deposition is directly pathogenic, and our knowledge of the full range of its histological and clinical expression will require the expansion of available published reports.

The long-term outlook for renal function in patients with C1q nephropathy is not clear. In patients with FSGS appear to have a more aggressive course. The nephropathy is frequently resistant to steroids or there are relapses.

In the present case no systemic alterations were detected and in the follow-up no there are LES criteria. Renal function is well one post-biopsy year, but proteinuria continue in spite of treatment with cytostatics.

See C1q Nephropathy in the chapter [Minimal change disease] (Text and atlas. Only in spanish).

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Bibliography

• Fukuma Y, Hisano S, Segawa Y, Niimi K, Tsuru N, Kaku Y, Hatae K, Kiyoshi Y, Mitsudome A, Iwasaki H. Clinicopathologic Correlation of C1q Nephropathy in Children. Am J Kidney Dis. 2006; 47:412-8 [PubMed link]
• Kersnik Levart T, Kenda RB, Avgustin Cavic M, Ferluga D, Hvala A, Vizjak A. C1Q nephropathy in children. Pediatr Nephrol. 2005;20:1756-61 [PubMed link].
• Nishida M, Kawakatsu H, Okumura Y, Hamaoka K. C1q nephropathy with asymptomatic urine abnormalities. Pediatr Nephrol. 2005;20:1669-70. [PubMed link]
• Lau KK, Gaber LW, Delos Santos NM, Wyatt RJ. C1q nephropathy: features at presentation and outcome. Pediatr Nephrol. 2005;20:744-9. [PubMed link]
• Sharman A, Furness P, Feehally J. Distinguishing C1q nephropathy from lupus nephritis. Nephrol Dial Transplant. 2004;19:1420-6. [PubMed link] [Free full text]
• Markowitz GS, Schwimmer JA, Stokes MB, Nasr S, Seigle RL, Valeri AM, D'Agati VD. C1q nephropathy: a variant of focal segmental glomerulosclerosis. Kidney Int. 2003;64:1232-40. [PubMed link]
• Jennette JC, Hipp CG. C1q nephropathy: a distinct pathologic entity usually causing nephrotic syndrome. Am J Kidney Dis. 1985;6:103-10. [PubMed link]
  

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