Board Thread:Theories and Speculation/@comment-25576506-20141211215919/@comment-945885-20141215030757

It's heavily implied that there were several clans descending from Kaguya, and at one time multiple clans even had the Byakugan, but it gradually got bred out. Only the Hyuga recognized the importance of preserving it, which allowed them to maintain the kekkei genkai by "keeping it in the family."