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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 20 000 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:
* Leukocoria : in the beginning a white reflection in the pupil or a
leukocoria can only be seen in certain directions and under certain lighting
conditions. Early signs can be seen with photos taken with a flash, but parents
might not be informed with regards to the significance of this white reflex.
*Strabismus: strabismus, even intermittingly, must never be considered
as "harmless" for an infant. This symptom should lead to an ophthalmological
examination with ocular fundus control.
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 IRM or an ocular sonogram .
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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.
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Unilateral retinoblastoma |
Bilateral retinoblastoma |
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Non hereditary form: |
Hereditary form : |
Hereditary forms: |
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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:
- review the family history of your child in order not to ignore any antecedents
of tumors in other members of your family. It is important to put an age to
the person who had a tumor. A family tree is drawn up taking into account the
background of your families going back to the child's grand parents.
- evaluate according to your child's personal tumoral and family background
the probability of a genetic predisposition to retinoblastoma. With this objective
in mind, it is important that you have available the results of your own ocular
fundus, which in principle will be requested during the time your child is being
treated.
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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Retinostop est une association loi 1901. Parution au JO du 1er mars 1995-page 927-n°1745 |
