In addition, FMRP (Fragile-X Mental Retardation Protein) KO mice, a model of Fragile-X syndrome, also exhibit a significant increase in the density of thin and long dendritic spines as well learning and memory deficits (Comery et al., 1997; Irwin et al., 2000; McKinney et al., 2005; Dölen et al., 2007). Here, FMR1 is linked to fragile X syndrome.