The composition and concentration of these products is influenced by numerous factors, such as neuronal activity, circadian rhythm, biological sex and age.34–36 Among these, proteins such as Aβ, tau, α-synuclein, and huntingtin have gained particular attention because of their association with neurodegenerative conditions such as AD, Parkinson’s (PD) and Huntington’s disease (HD), respectively. The gene discussed is HTT; the disease is Parkinson disease.