Another RBP required is the Src-associated with a mitosis of 68 kDa (Sam68): knocking down Sam68 in neuronal cultures or interfering with its binding to β-actin mRNA causes a deficit of β-actin mRNA in dendrites and in spine density (122), while loss of Sam68 has been connected with the pathogenesis of neurodegenerative fragile X tremor/ataxia syndrome (FXTAS) (129,130). The gene discussed is ACTB; the disease is fragile X-associated tremor/ataxia syndrome.