Board Thread:Warhammer 40k General Discussion/@comment-37.152.33.225-20131108174133/@comment-6078851-20141010160807

once again lets journey to 'codex quote corner' :P - codex: blood angels:

"... he (sanguinius) was also gifted with the power of prophecy, able to see visions of what lay ahead. it is almost certain that he knew he was going to his death when he boarded horus' battle barge and yet he went anyway."

"although it is known to but a few, the blood angels are a dying chapter, for they suffer from a dreadful flaw. this chapter, once the most golden and blessed of all the chapters, now shuns the company of its fellows where possible. some, it is said, are driven by a terrible death-seeking madness, brought on by visions of the death of their primarch. others are afflicted by the terrible red thirst, a craving for blood which some claim may be the first signs of a descent into chaos."

"some say that it is because sanguinius was more touched by chaos than the others during his flight through the warp. they cite the fact that he possessed wings - an obvious mutation - to support their case. their argument runs that the gene-seed extracted from him was flawed even before the first blood angels were created, and thus terrible consequences were preordained. others deny this, citing that the emperor himself trusted the winged primarch implicitly, and oversaw the creation of the blood angels. certain heretics counter this with the argument that the emperor also trusted horus..."

so even the codex isn't explicit as to the origins of sang's wings.