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Developmental delay, mental retardation and learning disability in the family |
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General introduction |
Developmental delay, which can be of varying degrees of severity, has many causes.
In some cases the cause is known, but in most it is unknown.
Actual mental retardation occurs in approximately 1% of school-age children.
Learning disabilities at various levels (special classes, etc.) are more frequent and affect
about 10% of children.
These problems are more common in boys than in girls.
The causes of developmental delay and mental retardation are multifactorial, meaning that the risk
for having a retarded child cannot be estimated unless the exact diagnosis is known.
It is important to note that most cases are not hereditary (genetic), but the result of environmental
factors.
In cases where there are a number of affected family members, the likelihood that this family has a
genetic problem is greater.
Moreover, if there are certain findings that indicate a specific syndrome of which mental retardation
is a part, the picture is more ominous.
Mentally retarded adult family members may not have been diagnosed genetically.
Therefore in many families the cause of the mental retardation is unknown.
It is thus important to ascertain all the medical details of any retarded family members before or
immediately after the beginning of pregnancy in order to establish the degree of risk more precisely.
If these family members have not undergone genetic testing, it is worth referring them for
examination by a geneticist, since this may lead to recommendations for appropriate tests that the
couple concerned should undergo.
Although it may seem surprising, the geneticists clinical examination is very important, because he
can evaluate with a significant degree of precision whether the condition is inherited and what the
risk is for other family members to have a child with a similar problem.
It is important to note that all couples are at risk for having a child with developmental delay, even
without a family history, but in most cases this cannot be diagnosed in advance.
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What is your risk for having a child with developmental delay if there are other affected family members? |
In order to evaluate your risk, it is important to know how the patient is related to you and what
is the exact diagnosis of his/her condition.
- If it is your child (a joint child or the child of one of the partners from a previous marriage)
and a precise diagnosis has not yet been made, you should be referred to a genetic institute as
soon as possible for a genetic evaluation and so that the child can be examined clinically.
In any event, if you are pregnant, it important for you to undergo testing for carrier status of
fragile X syndrome.
This syndrome is a common cause of mental retardation, and it is important to do this test even
in cases when the diagnosis of your child is already known.
- If it is a family member on the fathers side, it is also important to find out whether genetic
testing has been performed and what the diagnosis was.
If an exact diagnosis is known, it is advisable to refer to a genetic institute for an exact
evaluation of your risk.
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If the diagnosis is unknown and there are a number of affected relatives on the fathers
side, especially if a first degree relative (the fathers siblings or parents) is affected,
genetic testing is strongly recommended.
If this is not feasible and you know that the patient has not undergone chromosome
testing, it is important for the physician to refer the father to a genetic institute
for chromosome testing.
The couple should bring details about, and pictures of the relative with the defect
to the consultation.
When the patient is a member of the fathers family and the result of chromosome testing
on the father is normal, the risk for that couple to have a mentally retarded child is no
greater than that which exists in the general population.
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The couple should return to the genetic institute after receiving the results of the chromosome test
so that they can receive accurate counseling.
If there is no known diagnosis for the patient and he/she is a second-degree or more distant relative,
the same procedure is followed, even though the couples risk of having a mentally retarded child is much
lower.
- The situation is different if the affected relative is a member of the mothers family:
- If the affected individual is a member of the mothers fathers family:
Firstly, it is important to find out whether genetic testing has been carried out and, if so,
what was the diagnosis.
Whether or not the precise diagnosis is known, the couple should be referred to a genetic institute.
If the diagnosis is known, then the genetic counselor can evaluate the extent of the risk of
having a mentally retarded child.
If the diagnosis is not known and there are a number of affected relatives in the family,
particularly first-degree relatives (brother, sister or parent of the mothers father), it is
recommended that these affected individuals be tested in a genetic institute.
If this is not possible, and it is known that the patient has not undergone chromosome testing,
it is important that the wife be referred to a genetic institute for chromosome analysis and
testing for carrier status of fragile X syndrome.
If the results of both of these tests are normal, then the couple is not at a significantly
higher risk than the general population for having a mentally retarded child.
The couple should return to the genetic institute after receiving the results of the
chromosome test, if possible bringing with them details and pictures of the affected relatives,
so that they can receive accurate counseling.
If the affected family members are second-degree or more distant relatives and the diagnosis
is not known, the same procedure is followed, even though the couple�s risk of having a
mentally retarded child is much lower.
- If the affected individual is a member of the mothers mothers family:
It is important to check whether the problem affects females only or both males and females.
If either of these is the case, see section 1 above (where the affected relative is on the
mothers fatherï side).
If the problem only affects males, then it is important that the family undergo genetic
investigation including physical examination of the patient.
This is because there is a possibility that the condition present in this family is a
genetic syndrome that is transmitted by X-linked inheritance.
In this form of inheritance, only males are affected.
The X chromosome has a number of genes that cause mental retardation, for some of which tests
are available, and these can be performed in families with many affected members.
Even if the patient cannot be brought to the genetic institute, it is important that the
couple concerned undergo counseling.
They should bring with them the patients medical documents and also pictures in order to try
to arrive at a diagnosis and evaluate the risks.
Even if it is not possible to perform genetic testing on the patient, it is important for the mother
to undergo chromosome analysis and testing for carrier status of fragile X syndrome.
It is important to emphasize that if the patient cannot
be examined, the risk for the mothers sons to be affected cannot be eliminated.
In all cases of mental retardation affecting only the males in the mothers mothers family, it is important
that the couple be referred for counseling at a genetic institute.
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