It's not very new research. It's been known for a long time that this class of compounds is transported by a particular mechanism that's presumably there to protect the brain. A lot of drugs are pushed out of the brain by this transporter. No, this is just one possible explanation for why some people seem to be particularly susceptible, with their genetic variance of this, which would explain why some people might get very high levels of mefloquine in their brain.
There are other risk factors, too. It's not mefloquine or PTSD. It's perfectly possible that mefloquine and PTSD could occur in an individual, along with other symptomatology. That's the nature of neuropsychiatric problems: depression, anxiety and things of this sort. They rarely travel alone. You have the concept that mefloquine can travel on its own, but also, as a risk factor, contribute to neuropsychiatric problems. That doesn't mean it's unimportant, but that the context of mefloquine use is very important. Obviously, the military are exposed to extremely stressful situations in some cases, and there could well be an interaction between that exposure and the drug. Without the drug, maybe the interaction wouldn't result in a long-term, chronic, neurotoxicity.