Spine Morphology and Plasticity in X-linked Mental Retardations

In the past several years, a multitude of genes has been linked to mental retardations in humans, in particular the most commonly occurring X-linked mental retardations. An emerging idea is that structural and functional abnormali- ties in spines and synapses are a common feature of mental retardations. Consistent with this concept, a number of genes that control synaptic function have been implicated in X-linked mental retardations. In this review we discuss aberrations in spine and synapse structure and function in X-linked human mental retardations and corresponding mouse models with mutations in genes that modulate synaptic structure and function. A thorough understanding of these synaptic structures and abnormalities would enhance our knowledge of the normal process of learning and understand how synaptic aberra- tions contribute to cognitive deficits such as those observed in mental retardations.