Some results indicated that serum BDNF was reduced in manifested HD patients compared to healthy controls [85], consistent with a reduction in BDNF mRNA [86]; however, neither its transcript nor protein showed differences in other studies between controls, pre-symptomatic and symptomatic individuals [82,87,88], as several factors can influence BDNF concentration (e.g., sex, age, inter assay variations, instability of BDNF after plasma/serum collection and preparation) [83]. The gene discussed is BDNF; the disease is Huntington disease.