Some studies have reported that low levels of both phosphorylated tau at threonine 181 (p-tau) and the p-tau:t-tau ratio in CSF may differentiate TDP-43 and tau subtypes of FTLD (159–162), but these findings seem to be driven by the higher levels of t-tau in patients with ALS (162–164) and not by lower levels of p-tau in FTLD-TDP (165). This evidence concerns the gene MAPT and amyotrophic lateral sclerosis.