PTN and Alzheimer disease: In the validation set, PTN 151–166 correlated with t-tau in the control group (rs, = 0.629, p = 0.03) and in the PD group (rs, = 0.515, p = 0.05), and with P-tau in the control group (rs, = 0.656, p = 0.02), in the AD group (rs = 0.514, p = 0.05), and in the PD group (rs = 0.564, p = 0.03), and with t-tau only in the PD group (rs = 0.515, p = 0.05), while it did not correlate to Aβ42 in any group.