Updated on 14/12/2008

Retinoblastoma

  1. The disease
  2. Genetic predisposition

The disease

Retinoblastoma is a cancer tumor of the retina. The diagnosis is most oftentimes made before the age of 5. This disease affects 1 per 15 to 20000 live births. The treatments are increasingly effective and suited to each individual case and enable 90% of children to be cured in industrialized countries.

Clinical signs of the disease include:

Diagnosis of retinoblastoma is based essentially on an examination of the ocular fundus under general anesthesia. This enables the number of tumors, the size of the tumors, their position and the presence or not of vitreous. Seeding to be ascertained. The examination may be completed by a scanner an MRI or an ocular sonogram.

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Genetic predisposition

Retinoblastoma, as with all tumors, develops from a cell which has been affected by a genetic alteration. Our genetic base is found in practically all our cells which is made up of approximately 30 000 genes in duplicate copies (one copy inherited from each parent). In the case of retinoblastoma, we know that both copies of the RB gene need to be altered to develop a tumor.

In more than 50% of the cases, retinoblastoma affects one eye (unilateral retinoblastoma). In the great majority of cases (90%), both copies of the RB gene are altered within a retina cells developping during early childhood.

In under 50% of the cases, retinoblastoma affects both eyes (bilateral retinoblastoma: the child is affected by several independent retinal lesions. In this case, we immediately deduce a genetic predisposition meaning that the child carries an alteration of the RB gene in all her/his cells including the retina cells (constitutional alteration). The second copy of the RB is altered in the retina cells. It is to be noted that 10% of children with unilateral retinoblastoma have a genetic predisposition.

As such, heriditary forms of retinoblastoma include 10% of unilateral retinoblastomas and all bilateral cases.

In 25% of the cases, one of the two parents had retinoblastoma as a child or has retinoblastoma scars which have spontaneously involuted. Children who have inherited the constitutional alteration of the RB gene from one of the parents has a 50% chance of transmitting this alteration to each of his/her offspring children.

In 75% of the cases in which there is no family history, the mutation occurred in the germ cells (sperm and egg cells) of one of the two parents. In this case, there is little chance of brothers and sisters of the affected child having a predisposition to the disorder. However, the child with a predisposition to retinoblastoma has a 50% of transmitting the alteration to his/her offspring.

For all patients with retinoblastoma, there are different risk levels of being a carrier of the constitutional alteration of the RB gene and thus a predispositional risk for the siblings and the offspring of the patient. In the absence of a genetic study, early and frequent monitoring is recommended for all children with a genetic predisposition to retinoblastoma with an ocular fundus examination up until age 5.

Retinoblastoma forms and associated statistics
Unilateral retinoblastoma
More than 50% of the cases
Bilateral retinoblastoma
Under 50% of the cases
Non hereditary form:
90% of unilateral cases
Hereditary form:
10% of unilateral cases
Transmission risk: 50%
Hereditary form:
100% of bilateral cases
Transmission risk: 50%

DNA testing of the RB gene is advised for all children affected by retinoblastoma and adults who were treated during childhood. Two blood samples are collected for the study and are used to detect the possible presence of mutations in the RB gene.

This research takes several months to carry out. If the results come out negative (if no alteration is found in the RB gene) technical limits would lead to conclude that the results are not very informative. The risk of a genetic alteration existing are decreased, but not completely. (especially in the case of unilateral retinoblastoma. However, if a genetic alteration is identified, this becomes the basis for genetic testing to be proposed to all other family members. In this case, a negative result is significant.: if the subject tested is not a carrier of the identified predisposition in the family and if he/she is under 5 years old, he/she no longer needs ophthalmology monitoring. Generally speaking, the objective of RB gene DNA testing is to monitor the affected child, but also the siblings, first cousins and then later on his/her offspring.

Your child is monitored for retinoblastoma, and you have been advised or upon your initiative to contact a genetic therapist for genetic counselling. The genetic therapist during this consultation, together with you, shall attempt to:

In a large number of cases, genetic counselling will be proposed for your child in view of initially analyzing the RB gene. The consent of both parents will therefore be required. While the presence of both parents is not necessary, the absent parent can forward the consent document to the Genetics department. It is up to the parents to request genetic counselling at an appropriate genetics facility near their home.

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