Tau is a family of six isoforms, derived from a single gene by alternative mRNA splicing[1]. They vary in size from 352 to 441 amino acids (3[6].8 to 4[5].9 kDa), and differ from one another in having three or four microtubule binding repeats (R) of 31-32 amino acids each, and two, one or none amino terminal inserts (N) of 29 amino acids each[2].