WEEK 1 CELLULAR BIOLOGY AND ALTERATIONS.

• Retinoblastoma is a rare cancer that occurs only in children. It develops either as a hereditary disease, due to an abnormality of the RB1 gene, or sporadically (70% of cases). Located on chromosome 13q14, the RB1 gene is responsible for encoding pRb, which is a tumor suppressor protein. In the heritable form, the RB1 gene mutation is inherited through germinal cells, with a second mutation occurring in somatic retinal cells. The noninherited type of retinoblastoma occurs as a result of two mutations in the somatic retinal cells. The tumor arises from the inner surface of the retina and then spreads into the retina, resulting in leukocoria—a white appearance to the red reflex, commonly called cat-eye reflex—which is most often first identified by the child’s parents. • Normally the RB1 gene (pRB) governs the passage of the restriction point in the cell cycle, thus regulates cell proliferation. Germline mutations are inherited, whereas somatic mutations are acquired.