GDNF and early-onset autosomal dominant Alzheimer disease: The potency of neurotrophic factors, particularly NGF, BDNF, CNTF and GDNF, in promoting neuronal survival has raised much hope for their therapeutic use in neurodegenerative diseases including Alzheimer’s disease, Huntington’s disease, amyotrophic lateral sclerosis (ALS), Parkinson’s disease and glaucoma [2,3,4].