There is an age-dependent decrease in BDNF expression in the major sources of the afferents to the striatum. BDNF mRNA is progressively reduced in the cerebral cortexes and subcortical sources of striatal afferents, including inputs from the thalamus and the midbrain. The loss of BDNF plays an important role in motor and nonmotor abnormalities in Huntington’s disease and contributes to striatal neurodegeneration. This evidence concerns the gene BDNF and juvenile Huntington disease.