Board Thread:Theories and Speculation/@comment-5119417-20150524174321/@comment-734582-20150528125035

Sarutobii2 wrote: From ShonenSuki's translation of the third databook:

If one spends a lot of time and trains one's chakra over and over again, this technique can be invoked.'

This can also be read as "you need to train a lot before you can use it", unlike e.g. Amaterasu which can be used from the start.

However, since Sasuke has Amaterasu and Itachi has Amaterasu, it's clear that these powers are not unique. Furthermore, since there are apparently only six Mangekyou users (madara, his brother, obito, sasuke, itachi, sishui) it's not exactly a large group to draw conclusions from. For all we know, these powers are "mini-kekkei genkai" and similar by blood.