In the preclinical and very early stages, TGF-β1 level is high (similar to the control group) and then gradually decreases with the severity of symptoms; hence the hypothesis that in the first stages of HD (preclinical and very early), TGF-β1 has a neuroprotective effect that gradually diminishes in the symptomatic stages of the disease as plasma levels of TGF-β1 decrease. This evidence concerns the gene TGFB1 and Huntington disease.