cognitive disorders such as adhd, autism, intellectual disability, and fragile x syndrome, may be resultant from abnormalities in dendritic spines, especially the number of spines and their maturity. the ratio of matured to immature spines is important in their signaling, as immature spines have impaired synaptic signaling. fragile x syndrome is characterized by an overabundance of immature spines that have multiple filopodia in cortical dendrites.