The presence of AChEis causes the neurotransmitter to hang around and fire excessively, and therefore can cause abnormal brain function and uncontrolled muscle action.
Another study found that among veterans, those who were sick were more likely to have a genetic variation that means their bodies are less able to detoxify AChEis.
AChEis are found in pesticides that were used to protect soldiers against sand flies and other insects, and in the pyridostigmine bromide pills given to soldiers as part of a pre-treatment against nerve agents.