The BDNF protein levels are decreased in saliva while BDNF-promoter methylation is increased in the blood in Huntington’s disease subjects when compared to controls. Salivary BDNF measures may represent an early marker of disease onset and DNA methylation at the BDNF promoter IV could be a biomarker of psychiatric symptoms in Huntington’s disease patients. This evidence concerns the gene BDNF and Huntington disease.