IgA nephropathy combined with thin basement membrane nephropathy in children

IgA Nephropathy (IgAN) and thin basement membrane nephropathy (TBMN) are the most common and important causes of persistent hematuria in childhood, and with great interest I have read the published article by Hwang et al [1] that appeared in a recent issue of Kidney Research and Clinical Practice entitled “Clinical manifestations of IgA nephropathy combined with thin glomerular basement membrane nephropathy in children”. In this study, the authors reported that TBMN is frequently combined with IgAN (15.8%) and that patients with mixed IgAN and TBMN have better renal pathology and less proteinuria compared to those with isolated IgAN. I would like to point out several issues regarding this study. First of all, the coexistence of IgAN and TBMN was not clear because nonspecific focal basement membrane thinning may be associated with IgAN. A variety of methods are used to measure the glomerular basement membrane (GBM) thickness, and considerable variations can be produced during the preparation of electron microscopy specimen. Coleman et al [2] reported that some specimens from the patients with minimal change disease revealed an artefactual thinning of GBM. GBM thinning is also associated with some inherited defects. However, this study did not include the family history of hematuria. Second, it is not reasonable to conclude that the combined thinning of GBM may have a better prognosis in patients with IgAN. Although the patients with mixed IgAN and TBMN have less proteinuria than those with isolated IgAN, the authors’ conclusion was derived from their cross-sectional study, but not based on a longitudinal study design. Previous studies also had inconsistent results. Data from China show no significant differences in follow-up serum creatinine and estimated glomerular filtration rate between patients with IgAN and TBMN and those with isolated IgAN [3]. According to a review from Norby and Cosio [4], the combination of TBMN generally does not present a poor prognosis in glomerular diseases. Longitudinal studies are required to draw a conclusion about the significance of combined TBMN in IgAN.