Ruinbound Dwarves are a sub-species of Dwarf that are occasionally born in the Mror Holds, to any clan (and not requiring the parents to be ruinbound). This is a recent development, the first ruinbound children were born only 30 years ago, making all of them children in the eyes of the Mror. The different clans all have differing views on the ruinbound, but none can say why they happen with any certainty. Clan Doldarun asserts that they are children corrupted by Dyrrn, the Corruptor in the womb. Clan Narathun argue that they may be a result of energy emanating from Sol Udar influencing the developing child, but there's no direct evidence tying them to any of the Daelkyr
Every ruinbound is born with a personal Symbiont, which cannot be separated from the child. They are permanently fused, and as they grow up together, the dwarf doesn't view the symbiont as a separate entity to themselves, it's more like an extra limb. Many ruinbound dwarves have disturbing mutations in addition to their symbiont sibling, making it impossible for many to hide what they are.