**Core Concept**
The question is testing the understanding of **immunoglobulin A (IgA) nephropathy**, a type of **glomerulonephritis** characterized by the deposition of IgA antibodies in the glomeruli. This condition is also known as **Berger's disease**. The underlying principle involves the abnormal deposition of **immune complexes**.

**Why the Correct Answer is Right**
IgA nephropathy is indeed characterized by the mesangial deposition of electron-dense substance, which represents the accumulation of IgA immune complexes. This deposition leads to the activation of **complement pathways** and the recruitment of **inflammatory cells**, resulting in **glomerular injury**. The **mesangium** is a critical area for the deposition of these immune complexes.

**Why Each Wrong Option is Incorrect**
**Option A:** This choice is incorrect because it does not accurately represent the condition characterized by mesangial deposition of electron-dense substance.
**Option B:** Similarly, this option does not align with the specific pathological features of IgA nephropathy.
**Option C:** This choice is also incorrect as it does not correspond to the mesangial deposition seen in IgA nephropathy.
**Option D:** This option is incorrect as it is not associated with the characteristic mesangial electron-dense deposits.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that IgA nephropathy is the most common cause of **glomerulonephritis** worldwide and often presents with **hematuria** following a respiratory or gastrointestinal infection.

**Correct Answer:** D. IgA Nephropathy.