Age of the Dragons
Dragonborn, along with Orcs, are a true race that did not originate from the Creators. They were bred from human stock by the dragons as the great winter approached. Each dragon has a clan of Dragonborn in his or her service. Sometimes members of other races will join these clans as well, but they are never truly considered Dragonborn (nor is there any sort of ritual to change their race – it is genetic).
Members of a Dragonborn horde would not likely be suitable for play (unless perhaps a Dragon or his Drake deal with people differently in a locale), but a defector or exile would be acceptable.
As in the PHB.