Unfortunately, no supplementary information is provided about the specific ways in which neurons are affected by problems with RNA binding which are caused by the mutated FMR1 gene. At a recent conference held by the National Fragile X Foundation, an intriguing lecture was given on brain imaging conducted on affected FXS individuals. The imaging is focused on the regions of the brain associated with temporal lobe structures known to be involved in mediating learning and memory, such as the amygdala and the hippocampus. This link between the hippocampus and the disease was supported by another study which analyzed the volumes of the hippocampus in affected versus non-affected individuals. Despite these hopeful findings, there is still much uncertainty surrounding the link between gene and behavior in the case of fragile X syndrome.
Mental retardation is characterized by a complex set of behaviors with a myriad of manifestations.
It is understandable, then, that the links between these two seemingly opposed elements of the disease have not yet been fully elucidated. The imaging data may present one connection, but there are likely many more which lie between cytological issues and MRI evidence on one side of the chain and between MRI evidence and mentally retarded behavior on the other side of the chain. And yet the particular subset of behaviors in question is all called mental retardation. For the time being, I think, it is safe to assume that the link between a single gene and a complex class of behaviors is strong for fragile X syndrome.