**Core Concept**
Seborrheic dermatitis, lytic skull lesions, ear discharge, and hepatosplenomegaly are classic symptoms of a rare genetic disorder characterized by abnormal cell membrane function and impaired phospholipid metabolism. This condition involves a defect in the cholesterol biosynthesis pathway, leading to the accumulation of toxic intermediates and subsequent cellular damage.

**Why the Correct Answer is Right**
The correct diagnosis is **Niemann-Pick disease type C (NPC)**. NPC is caused by mutations in the NPC1 or NPC2 genes, which encode proteins essential for the transport of cholesterol and other lipids within the cell. The accumulation of these lipids in the lysosomes leads to cellular dysfunction, resulting in the characteristic symptoms of seborrheic dermatitis, lytic skull lesions, ear discharge (due to chronic otitis media), and hepatosplenomegaly. The lytic skull lesions are a result of the accumulation of abnormal lipids in the bones, leading to bone resorption.

**Why Each Wrong Option is Incorrect**
* **Option A:** This is incorrect because while **Gaucher's disease** is a lysosomal storage disorder, it primarily presents with hepatosplenomegaly, bone pain, and anemia, without the characteristic skin and ear symptoms.
* **Option B:** This is incorrect because **Hurler's syndrome** is a mucopolysaccharidosis that presents with intellectual disability, clouded corneas, and characteristic skeletal abnormalities, but not the specific combination of symptoms seen in NPC.
* **Option C:** This is incorrect because **Tay-Sachs disease** is a lysosomal storage disorder caused by a deficiency of hexosaminidase A, presenting primarily with neurological symptoms and cherry-red spots on the macula, but not the characteristic skin and ear symptoms.

**Clinical Pearl / High-Yield Fact**
Niemann-Pick disease type C is a rare genetic disorder with a variable age of presentation, ranging from infancy to adulthood. Early diagnosis and treatment with miglustat or other chaperone therapies may help slow disease progression and improve quality of life.

**Correct Answer:** D.