**Core Concept**
Familial retinoblastoma is a rare, hereditary eye cancer that affects the retina, often presenting in children under the age of five. It is characterized by the mutation of the RB1 gene, which plays a crucial role in regulating cell growth and division.

**Why the Correct Answer is Right**
The RB1 gene acts as a tumor suppressor, preventing uncontrolled cell growth by inhibiting the progression from the G1 phase to the S phase of the cell cycle. In familial retinoblastoma, a germline mutation in the RB1 gene is inherited, increasing the risk of developing retinoblastoma. This genetic mutation can be passed down from an affected parent to their offspring, making it a dominant inherited trait.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not specify the genetic basis of familial retinoblastoma. While radiation and chemotherapy are treatments for retinoblastoma, they do not explain the underlying cause of the disease.
**Option B:** This option is incorrect because it mentions a viral cause, which is not supported by scientific evidence. Familial retinoblastoma is a genetic disorder, not a viral infection.
**Option C:** This option is incorrect because it refers to a different type of cancer, specifically neuroblastoma, which is a separate entity from retinoblastoma.

**Clinical Pearl / High-Yield Fact**
The RB1 gene mutation in familial retinoblastoma is a classic example of a tumor suppressor gene mutation, highlighting the importance of genetic screening in high-risk families.

**Correct Answer: D**