Another study used chitosan-coated lipid nanoparticle carriers conjugated to the transactivator of transcription (TAT) cell-penetrating peptide to enhance CNS delivery of glial cell-derived neurotrophic factor (GDNF) in a mouse model of PD, leading to decreased dopaminergic neuron loss and improved motor function (130). The gene discussed is GDNF; the disease is Parkinson disease.