There are various studies indicating that tau, ptau and tTau in CSF, is a candidate ALS biomarker148 or not.149,150 Studies have also shown CSF pTau/tTau ratio as an ALS biomarker,56,148,151 and this may be prognostic and diagnostic, differentiating patients with ALS from mimics.56 The type of tau in urine has not been investigated, but the size may restrict excretion. Here, MAPT is linked to amyotrophic lateral sclerosis.