Not all of the Aereni refugees sought shelter in the shadow of the Fingerbones. Some fully embraced Lhazaar culture, mingling with humans and creating a significant population of half-elves. The island of Orthoss is a haven for the Khoravar, and half-elves from across Khorvaire have found their way to the town of Blackrock. Notably, the Lhazaar lifestyle has attracted a number of members of House Medani and House Lyrandar over the centuries -- young rebels seeking an escape from the smothering traditions of their houses. Their blood has been spread across the island, and it has been spread quite thin -- but occasionally a child of Orthoss develops a dragonmark.
Source: Dragonshard Part 2