Dense deposit disease is seen in?
**Core Concept**
Dense deposit disease (DDD) is a type of glomerulopathy characterized by the deposition of electron-dense material in the subepithelial space of the glomerular basement membrane (GBM), leading to nephrotic syndrome and renal failure. This condition is associated with the alternative complement pathway and the presence of C3 nephritic factor.
**Why the Correct Answer is Right**
Dense deposit disease is caused by the abnormal activation of the alternative complement pathway, which results in the deposition of complement components, particularly C3b, in the GBM. The C3 nephritic factor, an autoantibody that stabilizes the C3 convertase of the alternative pathway, is often present in patients with DDD. This leads to the accumulation of electron-dense deposits in the GBM, causing damage to the glomerular filtration barrier and resulting in nephrotic syndrome and renal failure.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because DDD is not primarily associated with the classical complement pathway.
**Option B:** This option is incorrect because membranous nephropathy is characterized by the deposition of immune complexes in the subepithelial space, but it is not the same as DDD.
**Option C:** This option is incorrect because focal segmental glomerulosclerosis (FSGS) is a different type of glomerulopathy that is characterized by the collapse of glomerular capillaries and sclerosis of the tuft.
**Clinical Pearl / High-Yield Fact**
Dense deposit disease is often associated with the presence of a C3 nephritic factor, which is a hallmark of this condition. This factor can be detected by performing a serum assay for C3 nephritic factor.
**Correct Answer:** D. Dense deposit disease is seen in D.