I agree that it is a mistake by Gehena, because for gem, genome or enema there is a lot of difference.
The correct term is Gehenna. It is a word of Greek origin, it appears in the Holy Bible and Means hell, purgatory. Hell or Purgatory of the Jews.
gehema is incorrectly written, and should be written as "Gehenna" being its meaning: Valley of ancient Palestine, to the SO in Jerusalem, where the Israelites offered their sacrifices to Moloch.