Electron microscopy findings of renal biopsy shows permeation of the lamina densa of the glomerular basement membrane (GBM) by a ribbon-like, homogeneous, extremely electron-dense material of unknown composition. Which of the following is the likely diagnosis?

Dense-deposit disease (formerly called Type II MPGN) Excessive activation of the alternative complement pathway. Electron M/E - Permeation of the lamina densa of the GBM by a ribbon-like, homogeneous, extremely electron-dense material of unknown composition. By immunofluorescence, C3 is present in irregular granular or linear foci in the basement membranes on either side but not within the dense deposits. C3 is also present in the mesangium in characteristic circular aggregates (mesangial rings). IgG is usually absent, as are components of the classical pathway of complement activation (such as C1q and C4).