C1q nephropathy in a 2-year-old boy presenting with steroid resistant nephrotic syndrome.

We experienced a case of a 2-year-old boy, who presented with steroid resistant nephrotic syndrome, which developed insidiously. Renal biopsy revealed that he had focal and segmental glomerulosclerosis on light microscopy, dominant mesangial deposition of C1q by immunofluorescent staining, and electron dense deposits on electron microscopy, which are all compatible with C1q nephropathy. He had no clinical sign of any collagen diseases, including systemic lupus erythematodes. So, the diagnosis of C1q nephropathy was made. An intensive treatment by a combination of cyclosporine, prednisolone and methylprednisolone pulse therapy was successful in achieving remission and disappearance of proteinuria in this patient. Although he developed hypertension requiring calcium blocker and angiotensin converting enzyme inhibitor, his renal function stayed within normal limit for 3 years after the initiation of the treatment. The growth was well preserved during the 3 years of treatment with almost unchanged SD scores for height. He has delay in speech, which may not be associated with the etiology of his nephropathy, based on the absence of such association in the previous reports. C1q nephropathy is still a controversial clinical entity, so accumulation of the cases may help further understand the pathogenesis and clinical manifestation of C1q nephropathy.