C1q nephropathy in the pediatric population: pathology and pathogenesis.

C1q nephropathy was originally described nearly 25 years ago by Jennette and Hipp. Since that time there have been a limited number of publications on C1q nephropathy, most of them in the pediatric literature. Despite reported incidences as high as 16% in some pediatric biopsy series, a consensus definition on the diagnosis of C1q nephropathy is lacking and its existence as a distinct clinical disease entity remains controversial. The purpose of this review is to discuss the biology of C1q in the context of mechanisms of C1q deposition, and to provide a detailed analysis of the published pediatric case series with a focus on the pathological criteria used to establish the diagnosis of C1q nephropathy as well as long-term outcomes in children.