In addition to the 3′ splice site at the end of exon 6, there are two alternate 3′ splice sites within exon 6 itself, termed “6P” and “6D” according to location (Fig. 1). Use of either of these splice sites results in a frame shift that introduces a unique amino acid sequence, PCCVPRATFLS (6P) or FWSKGDETQGG (6D), followed by a stop codon. As a result, tau 6P and 6D isoforms are truncated, lacking part of the proline-rich region, the MTBR region, and C-terminus