i think madara transplanted nagatos eyes at a young age to have the rennigan activated, cause i would imagine it takes an uzumaki to activate them. seemings the sage of the six paths was in fact a uzumaki. now how he got the eyes is another story ... but if madara in fact did GIVE nagato the rinnigan its cause he had the eyes, and nagato had the blood. honestly those are the only 2 uzumakis that are alive in the manga that we know about. idk what happened to his clan or even if there were more than a few. but madara found one and used him. i mean he couldnt have used naruto and besides narutos mom i dont think the manga mentions any other uzumakis.
and i would like to know why naruto kept his moms last name and not his dads. why the big secret with him and the 4th hokage, why couldnt he know that was his father. i mean he was gonna find out anyways. why tourcher the kid.