**Core Concept**
Alport syndrome is a genetic disorder characterized by glomerulonephritis, end-stage kidney disease, and hearing loss due to mutations in the COL4A3, COL4A4, and COL4A5 genes. These genes encode type IV collagen, a crucial component of basement membranes in the kidney and ear.

**Why the Correct Answer is Right**
The mutations in Alport syndrome lead to the production of abnormal type IV collagen, which disrupts the normal function of the glomerular basement membrane and the cochlear basement membrane. This results in progressive kidney disease and hearing loss. The disease is typically inherited in an X-linked pattern, affecting males more severely than females.

**Why Each Wrong Option is Incorrect**
**Option A:** Alport syndrome is caused by mutations in the COL1A1 and COL1A2 genes.
* Incorrect because Alport syndrome is caused by mutations in the COL4A3, COL4A4, and COL4A5 genes, not the COL1A1 and COL1A2 genes, which are associated with osteogenesis imperfecta.

**Option B:** Alport syndrome is characterized by skeletal abnormalities.
* Incorrect because while some patients with Alport syndrome may have skeletal abnormalities, this is not a primary feature of the disease.

**Option C:** Alport syndrome is a form of IgA nephropathy.
* Incorrect because Alport syndrome is a distinct genetic disorder caused by mutations in the COL4A3, COL4A4, and COL4A5 genes, not a form of IgA nephropathy.

**Clinical Pearl / High-Yield Fact**
Alport syndrome is often diagnosed in childhood or adolescence due to the presence of hematuria, which is a hallmark symptom of the disease. Patients with Alport syndrome may also experience hearing loss, which can progress to complete deafness in some cases.

**Correct Answer:** D.