AN experimental cancer drug can improve learning and memory in mice with fragile X syndrome (FXS), according to a new study published in a recent issue of Science Translational Medicine. The findings offer new hope to patients with FXS, the most common cause of inherited intellectual disability and autism spectrum disorder, which currently lacks an effective treatment.
Mutations in the fragile X mental retardation (FMR1) gene lead to loss of FMRP, a protein that regulates the expression of many genes in neurons. FMRP deficiency is known to impair neural stem cells’ ability to generate new neurons in the adult brain, but how this occurs was not fully understood. Studying a mouse model of FXS, Yue Li and colleagues found that loss of FMRP led to greater activation of neural stem cells, enhancing their differentiation into astrocytes but not neurons. The researchers identified the enzyme MDM2 as a key target of FMRP in neural stem cells. FMRP deficiency led to greater MDM2 activity, resulting in enhanced neural stem cell proliferation but reduced differentiation.
A specific MDM2 inhibitor known as Nutlin, currently in an early clinical trial for retinoblastoma, seemed to correct this imbalance between neural stem cell proliferation and differentiation. Low doses of Nutlin restored spatial memory and learning in FMRP-deficient mice, opening the door to repurposing the drug as a potential treatment for FXS.
