Board Thread:Warhammer 40k General Discussion/@comment-3416287-20150401101244/@comment-25177957-20150401210151

There's a difference between abhumans and mutants, by all technical means the abhumans have a mutated human genome mutated during the Age of Strife, but since their worlds are allied with the Imperium, the abhumans are tolerated, although mistrusted in the Imperial Guard.

Now a mutant as described by the Imperium is a person who has been mutated due to Chaos or Xenos taint, for example, a mutant hybrid which is part of a genestealer cult. Mutant aliens are hardly trusted by even the Tau and Eldar, and mutant xenos such as the Laer were responsible for worshipping Slaanesh, which led to the downfall of the Emperor's Children legion, and not to mention that the Inqusition also fears mutant xenos such as genestealer hybrids hiding amongst the Imperial populace.