**Question:** Hereditary retinoblastomas

A. Autosomal dominant inheritance
B. Allelic with non-hereditary retinoblastomas
C. X-linked recessive inheritance
D. Mitochondrial inheritance

**Core Concept:** Retinoblastoma is a malignant tumor of the retina, which develops from retinal pigment epithelium or retinal stem cells. There are two main types: hereditary and non-hereditary. Hereditary retinoblastoma can be caused by mutations in either of the following genes:

**Why the Correct Answer is Right:**
Choice C (X-linked recessive inheritance) is the correct answer because retinoblastoma due to mutations in the RB1 gene follows this pattern of inheritance. The RB1 gene is located on the X chromosome and provides instructions for producing a protein called retinoblastoma protein (pRb). Mutations in the RB1 gene cause the absence or dysfunction of pRb, which results in uncontrolled cell growth and formation of tumors.

**Why Each Wrong Option is Incorrect:**
A. Autosomal dominant inheritance (A) is incorrect because retinoblastoma caused by mutations in the RB1 gene follows an X-linked pattern, not autosomal dominant. Autosomal dominant inheritance would imply that both parents would have a 50% chance of passing the mutated gene to their child, which is not the case in retinoblastoma.

B. Allelic with non-hereditary retinoblastomas (B) is incorrect because the two types of retinoblastoma (hereditary and non-hereditary) are distinct entities with different genetic etiologies. Hereditary retinoblastoma is caused by mutations in the RB1 gene, while non-hereditary retinoblastoma is caused by mutations in the other retinoblastoma and شبكی کلی (RB) gene.

D. Mitochondrial inheritance (D) is incorrect because retinoblastoma is caused by mutations in the RB1 gene, which is located on the X chromosome and is not associated with mitochondrial inheritance patterns.

**Clinical Pearls:**
1. Non-hereditary retinoblastoma is caused by mutations in the شبكی کلی (RB) gene, which is located on chromosome 13. This type of retinoblastoma is more common in children and occurs sporadically, meaning it is not inherited from parents.
2. Familial retinoblastoma is caused by mutations in the RB1 gene, which is located on chromosome X. It is an X-linked dominant disorder, meaning that if a mother carries the mutated gene, there is a 50% chance of passing it on to her affected son or daughter, but only a 25% chance to an unaffected child.

**Explanation of the question:**
This question tests the understanding of the genetic basis of retinoblastoma and the difference between familial and non-familial forms of the disease. The correct answer (C) highlights the difference between the chromosomal locations and inheritance patterns of the RB gene in familial and non-familial retinoblastoma.