Glomerular Galactose-Deficient IgA1(KM55) Positive May Predict Poorer Prognosis in Coexisting Primary Membranous Nephropathy and IgA Nephropathy Patients

Primary membrane nephropathy (PMN) and IgA nephropathy (IgAN) are the most common glomerular diseases in China. Because of different pathogenesis, prognosis is significantly different. When the two diseases coexist (PMN/IgAN), the clinicopathological manifestations and prognosis remain unclear. In the present study, we analyzed the clinicopathological characteristics of PMN/IgAN patients, with only IgA deposition (PMN/IgA deposition) patients as controls. Galactose-deficient IgA1(KM55) and M-type Phospholipase A2 Receptor(PLA2R), both in circulation and renal tissues, were detected. Furthermore, prognosis of PMN/IgAN was explored. We found that PMN/IgAN also had some clinical features of IgAN in addition to PMN, such as higher serum albumin, along with a similar heavy proteinuria and lower titers of serum anti-PLA2R antibody. The positive rate of glomerular KM55 in PMN/IgAN was 23.5% (20/85), and 0% (0/29) in PMN/IgA deposition. Among those glomerular KM55 positive patients, KM55 and IgA colocalized mainly along the glomerular mesangial and capillary areas. Unfortunately, there was no significant difference in serum level of Gd-IgA1 between KM55+ and KM55- subgroups in PMN/IgAN patients, similar to the PMN/IgA deposition group. Notably, glomerular KM55 positive may predict a poorer prognosis in PMN/IgAN patients. In conclusion, our study suggested that, when glomerular KM55 staining was positive, this special coexisting PMN/IgAN disorder was prone to have more characteristics of IgAN besides PMN, and may predict poorer prognosis, while the mechanism requires further investigation.