Lead poisoning
Kane's ability to periodically obtain fresh meat, primarily in summer hunts with the Inuit, held off the most severe symptoms of scurvy. Franklin's expedition relied on the tinned foods (prepared in haste by Goldner), the poor soldering of which resulted in consistently high lead levels in the remains found to date. Lead poisoning would be a significant factor standing against their survival. While Kane's smaller party made hunting more practical, this difference was key to the respective outcomes of both expeditions.