C1q nephropathy: a true immune complex disease or an immunologic epiphenomenon?

We describe a 16-year-old Caucasian boy who presented with steroid-sensitive nephrotic syndrome aged 2 years. His clinical course was one of frequent relapses and severe steroid dependence. To manage this, he was sequentially treated with levamisole, then oral cyclophosphamide before being started on ciclosporin. A renal biopsy performed prior to commencement of ciclosporin confirmed minimal change disease on light microscopy. The immunohistochemistry and electron microscopy findings were in keeping with this. His complement levels were normal and his lupus serology negative. He remained on ciclosporin therapy for 8 years and had two further renal biopsies to detect ciclosporin-induced renal damage. Both biopsies showed evidence of increasing amounts of C1q deposition on immunohistochemistry and the presence of immune deposits on electron microscopy. As he had continued negative lupus serology, this was compatible with a diagnosis of C1q nephropathy. In addition both biopsies had changes compatible with chronic mild ciclosporin nephrotoxicity. This case is the first report describing in detail a paediatric patient with evolving C1q nephropathy who was treated successfully with rituximab. We discuss the role of C1q in this clinicopathological entity and question its significance.