Current status and issues of C1q nephropathy.
C1q nephropathy, first proposed by Jennette and Hipp [Am J Clin Pathol 83:415-420, 1985; Am J Kidney Dis 6:103-110, 1985], was described as a distinct glomerular disease entity characterized by extensive mesangial deposition of C1q, with associated mesangial immune complexes, and the absence of any clinical and laboratory evidence of systemic lupus erythematosus. Now, 20 years since the first report, the disease entity is gradually attaining recognition, particularly in the field of pediatrics. C1q is the subcomponent of C1 in the classical pathway of complement activation. Generally, C1q deposition is caused by the activation of C1 by immunoglobulin G (IgG) and IgM; therefore, C1q nephropathy is considered as an immune complex glomerulonephritis. However, in C1q nephropathy, it remains unclear whether the deposition of C1q in the glomeruli is in response to the deposition of immunoglobulin or immune complex, or whether deposition is non-specific trapping that accompanies increased glomerular protein trafficking associated with proteinuria. Since not only the pathogenesis of C1q deposition in glomeruli but also its significance are still uncertain, it has not yet been established as an independent disease. From recent publications of the clinical and pathological characterizations, C1q nephropathy has been thought to be a subgroup of primary focal segmental glomerular sclerosis. However, many reports describe different symptoms, histopathologies, therapeutic responses and prognoses, suggesting that C1q nephropathy is not a single disease entity, but that it may be a combination of several disease groups. There are many uncertain areas requiring further investigation, though it is hoped that a detailed examination of future cases will clarify the subgroups making up C1q nephropathy and their clinicopathological characteristics, and will lead to the establishment of C1q nephropathy as an independent disease entity.
Mii
Akiko
A
Department of Analytic Human Pathology, Nippon Medical School, 1-25-2 Nezu, Bunkyo-ku, Tokyo, 113-0031, Japan.
Shimizu
Akira
A
Department of Analytic Human Pathology, Nippon Medical School, 1-25-2 Nezu, Bunkyo-ku, Tokyo, 113-0031, Japan. ashimizu@nms.ac.jp.
Masuda
Yukinari
Y
Department of Analytic Human Pathology, Nippon Medical School, 1-25-2 Nezu, Bunkyo-ku, Tokyo, 113-0031, Japan.
Fujita
Emiko
E
Department of Analytic Human Pathology, Nippon Medical School, 1-25-2 Nezu, Bunkyo-ku, Tokyo, 113-0031, Japan.
Aki
Kaoru
K
Department of Analytic Human Pathology, Nippon Medical School, 1-25-2 Nezu, Bunkyo-ku, Tokyo, 113-0031, Japan.
Ishizaki
Masamichi
M
Department of Analytic Human Pathology, Nippon Medical School, 1-25-2 Nezu, Bunkyo-ku, Tokyo, 113-0031, Japan.
Sato
Shigeru
S
Central Institute for Electron Microscopic Researches, Nippon Medical School, Tokyo, Japan.
Griesemer
Adam
A
Transplantation Biology Research Center, Massachusetts General Hospital/Harvard Medical School, Boston, MA, USA.
Fukuda
Yuh
Y
Department of Analytic Human Pathology, Nippon Medical School, 1-25-2 Nezu, Bunkyo-ku, Tokyo, 113-0031, Japan.
D000293:Adolescent; D000328:Adult; D002648:Child; D002675:Child, Preschool; D015922:Complement C1q / Q000276:immunology*; D018450:Disease Progression; D019317:Evidence-Based Medicine; D005921:Glomerulonephritis / Q000145:classification / Q000276:immunology* / Q000473:pathology / Q000628:therapy; D006801:Humans; D007223:Infant; D007678:Kidney Glomerulus / Q000276:immunology* / Q000473:pathology; D011507:Proteinuria / Q000276:immunology; D012307:Risk Factors; D009626:Terminology as Topic; D055815:Young Adult
D015922:Complement C1q