## **Core Concept**
The clinical presentation described for the 8-year-old male, including non-blanching rashes (purpura) over the shin, swelling of the knee joint, significant hematuria (+++) and proteinuria (+), is highly suggestive of **Henoch-Schönlein Purpura (HSP)**, also known as IgA vasculitis. This condition is a form of systemic vasculitis that primarily affects small vessels and is characterized by the deposition of IgA immune complexes.

## **Why the Correct Answer is Right**
The correct answer, **C. IgA deposition**, is right because Henoch-Schönlein Purpura (HSP) is characterized by the deposition of IgA immune complexes in various tissues, including the skin, joints, intestines, and kidneys. The renal involvement in HSP can range from mild to severe and often presents with hematuria and proteinuria, as seen in this patient. The immune complexes deposit in the glomeruli, leading to an inflammatory response that can cause damage and the clinical manifestations observed.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is incorrect because while mesangial proliferation can be seen in various glomerulonephritis conditions, including IgA nephropathy (which is the renal manifestation of HSP), it does not specifically address the immune complex deposition that is characteristic of HSP.
- **Option B:** This option is incorrect because it mentions subepithelial humps, which are more characteristic of membranous nephropathy or certain types of immune complex-mediated glomerulonephritis, not typically HSP or IgA nephropathy.
- **Option D:** This option is incorrect because it refers to "no abnormality," which does not align with the significant renal symptoms (haematuria +++ and protein +) presented by the patient.

## **Clinical Pearl / High-Yield Fact**
A key clinical pearl is that Henoch-Schönlein Purpura (HSP) often presents with the classic tetrad of symptoms: **purpura**, **arthralgias/arthritis**, **abdominal pain**, and **renal involvement**. The presence of IgA deposition in the kidneys (IgA nephropathy) is a hallmark of HSP nephritis, making renal biopsy findings critical for diagnosis.

## **Correct Answer:** . **C. IgA deposition**