Developmental delay, mental retardation and learning disability in the family
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
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
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.
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.
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.
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.
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.
- 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
- 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 father- 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.
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.