You may have noticed that Anavex is not spending money on new clinical trials. That should give them the financial ability to go after AD with both the EMA and the FDA, especially since the content of the applications will heavily overlap. More importantly, they can try to time it so that their regulatory team won't be overbooked in more than one place at a time.
Ummm, How much do you think it costs to pursue an MAA or an NDA?
The company has $150 million.
Oh and by the way, orphan drug designation means that the FDA waves the NDA filing fee for Rett which is currently about $ 4 Million for 2024.
I'm not saying the compiling the data and organizing it for an MAA or NDA is a trivial task. Such a filing can be up to 100,000 pages. Much of a filing for one jurisdiction can be reused for another.
I think you are overestimating the cost of preparing an NDA submission.