**Question:** A patient with fibronectin mesangial deposits was diagnosed having fibronectin nephropathy. Which of the following is NOT true about fibronectin nephropathy?

A. Fibronectin nephropathy is a renal disease caused by the accumulation of fibronectin, a glycoprotein, in the mesangium of the glomerulus.
B. It is a rare disorder that affects both children and adults.
C. It is primarily caused by genetic mutations affecting fibronectin synthesis or degradation.
D. Treatment options include supportive care and corticosteroids.

**Correct Answer:** C. Fibronectin nephropathy is primarily caused by genetic mutations affecting fibronectin synthesis or degradation.

**Core Concept:** Fibronectin nephropathy is a rare renal disorder characterized by the accumulation of fibronectin, a glycoprotein, in the mesangium of the glomerulus. This leads to glomerular damage and dysfunction, resulting in proteinuria, hematuria, and progressive renal failure.

**Why the Correct Answer is Right:** The correct answer is "C" because fibronectin nephropathy is primarily caused by genetic mutations affecting fibronectin synthesis or degradation. This statement is true because genetic mutations in genes encoding for fibronectin or enzymes involved in its synthesis and degradation can lead to impaired fibronectin production or clearance, resulting in its accumulation in the glomerulus.

**Why Each Wrong Option is Incorrect:**

A. Fibronectin nephropathy is caused by deposition of immune complexes or deposition of immune complexes with subsequent mesangial proliferation. This option is incorrect because fibronectin nephropathy is primarily caused by genetic mutations, not immune complex deposition.

B. Fibronectin nephropathy can be treated with corticosteroids or immunosuppressive agents. This option is incorrect because the primary cause of fibronectin nephropathy is genetic mutations, and treatment focuses on managing the symptoms and slowing disease progression, rather than addressing the underlying genetic cause.

D. Fibronectin nephropathy is a clinical entity seen in children and adults. This option is incorrect as fibronectin nephropathy can affect individuals of any age, including children and adults.

**Clinical Pearl:** Fibronectin nephropathy is a rare clinical entity that should be considered in patients presenting with proteinuria, hematuria, and progressive renal dysfunction, especially in the context of a family history of similar renal diseases. A thorough clinical evaluation, including a detailed family history and renal biopsy, is crucial for the diagnosis. Once diagnosed, management involves supportive care, with close monitoring and management of complications such as hypertension and electrolyte imbalances. Genetic counseling is also recommended for affected individuals and their families.