**Core Concept**
ITGCN stands for IgA Nephropathy, also known as Berger's disease. It is a type of kidney disease characterized by the deposition of IgA antibodies in the glomeruli, leading to inflammation and damage. The IgA antibodies in ITGCN are primarily of the IgA1 subclass.

**Why the Correct Answer is Right**
ITGCN is a common cause of nephritis worldwide, accounting for up to 10% of all glomerulonephritis cases. The pathogenesis of ITGCN involves the deposition of IgA1 antibodies in the glomerular mesangium, which activates the complement system and leads to the recruitment of inflammatory cells. This ultimately results in glomerular damage and impaired kidney function.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect as ITGCN is not primarily associated with IgG antibodies.
**Option B:** This option is incorrect as ITGCN is not primarily associated with IgM antibodies.
**Option C:** This option is incorrect as ITGCN is not primarily associated with complement component 3 (C3) deficiency.

**Clinical Pearl / High-Yield Fact**
ITGCN often presents with hematuria, particularly after upper respiratory tract infections, and can progress to chronic kidney disease if left untreated. Early diagnosis and treatment with corticosteroids can improve renal outcomes in patients with ITGCN.

**Correct Answer: A. IgA Nephropathy.**