Mental retardation
The presence of a mental handicap in a given individual is determined by measuring its intelligence quotient (IQ). If one assumes that, in the general population, the mean IQ equals 100 and the standard deviation is 15, the following scale is in use since 1968 (World Health Organization) :
Severe mental retardation has an incidence of 1/250 newborn. Mild mental retardation could affect 3% of the general population.
However in this later case, it is difficult to identify the affected people when the IQ reaches 70 without the use of adapted tests.
These figures mean that in a country such as France (60 million people and 750.000 newborns each year), 3.000 children are born with a severe
mental handicap and 1,8 million people are mildly retarded.
One of the questions to answer for the clinicians in charge of this mentally retarded population, is whether the handicap is genetically
determined or not. It is clear that a number of events during the prenatal development, at birth or in the post-natal period can cause a
mental handicap. However, it is believed that 50% of the severe mental retardation is indeed genetically determined. A genetic determinant
to the mental retardation is also present when this handicap is inherited (familial cases with several affected individuals).
Mental retardation can be syndromic when it is associated with other clinical signs that are constantly present in affected individuals or non syndromic (or non specific) when mental retardation is the only constant clinical sign in affected patients.
For both types of mental retardation phenotypes, there is a significant genetic basis. The additional signs in the context of syndromic mental retardation can be malformations of the central nervous system. Such malformations are being recognized as an important cause of mental retardation with the development of improved medical imaging devices. The different situations that can be encountered are summarized in the figure below.
Our team has three main projects in this research field :
- Rett Syndrome pathophysiology (RS is a model of syndromic mental retardation)
- genetics of isolated cortical malformations (phenotypes, genotypes and epidemiology)
- investigation of syndromic cases of MR associated with a chromosomal rearrangement
Our team is composed of basic scientists and clinicians. In addition to our own activity, several international collaborations are established to access the best ressources available to achieve the proposed goals.. A detailed description of each project currently conducted in our team is presented in the "our projects"sections of this web site and a number of links to other sites dealing with mental retardation, genetics or cortical malformations is proposed in the Links section.