Retinoblastoma is a cancerous disease that affects babies and young children. With this disease, tumors are formed in the retina itself. Depending upon the placement and growth of the tumor in the retina, it is possible for the tumor to spead to the eye socket and/or to the brain via the optic nerve. It is usually diagnosed between birth and 5 years of age but can occur at any age. The most common symptom of the presence of retinoblastoma is a normally black pupil that appears white. This is often noticible with flash photography. Other symptoms include crossed eyes or eyes that do not track together, persistent eye pain, redness or irritation, and blindness or poor vision.
There are two types of retinoblastoma: heritable and nonheritable retinoblastoma.
Heritable retinoblastoma is a genetically inherited trait. It is controlled by a tumor supressor gene called RB1 which normally stops the abnormal growth of cells. When RB1 is deleted or mutated and does not function normally, cells can grow at an abnormal and uncontrolled pace. Much of the human genome is formed in duplicate. Although some genes are dominant, meaning a deletion or mutation in one copy of the gene will cause an effect, many genes are recessive, meaning both copies must be mutated or deleted for the effect to occur. For retinoblastoma to develop, both copies of the RB1 gene must be mutated or deleted. The first defective copy of the gene is passed on genetically in a dominant fashion which puts a baby at risk of getting the disease but the second copy is typically either mutated or deleted at some point early in life and/or development. If the second copy of RB1 is never mutated or deleted, tumors do not form and the individual is then a carrier of the gene. In contrast, nonheritable retinoblastoma occurs when both copies of RB1 are mutated after conception, this means that no defective gene is passed on from the parents.
Typically, patients with the hertitable form of retinoblastoma form a tumor in both eyes whereas the nonheritable patients typically form a tumor in just one eye. This is of course, not absolute. Patients with hertiable retinoblastoma can form a tumor in one eye and patients with the nonheritable version can have tumors in both eyes.
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