Clinicopathological study of IgA nephropathy in patients with congenitally reduced nephron mass

In experimental animal models, a reduction in the number of functioning nephrons is considered to play a role in the progression of glomerular injury. In human renal diseases, however, whether a superimposed reduction in the number of nephrons causes the exacerbation of preexistent glomerulopathy has not been elucidated. We herein report the results of a clinicopathological study of five patients with IgA nephropathy (IgAN) which occurred in a reduced nephron mass status (four cases of congenital solitary kidney and one case of bilateral hypoplastic kidneys). Four of the five patients had chronic renal failure (CRF) and exhibited a relatively rapid course to CRF as primary IgAN. Renal biopsy revealed that all four of the patients with CRF had glomerular hypertrophy and focal segmental glomerular sclerosis. In addition, two of them had a focal active lesion. In one patient with bilateral hypoplastic kidneys renal biopsies were performed twice in eight years. During this period her creatinine clearance deteriorated from 60.0 ml/min to 20.7 ml/min. Her first renal biopsy showed mild mesangial proliferation without sclerotic lesions, glomerular hypertrophy and mesangial IgA deposition, while all of them were prominent in the second renal biopsy. These observations suggest that IgAN superimposed on a nephron loss status may be frequently associated with a progressive course of disease, and careful follow-up and early treatment should be considered in such a condition.