I assume by AIP you mean "acute intermittent porphyria" as there are all kinds of conditions using the same acronim...?
From a lot of digging around, it seems there is a remote chance if can cause strange behaviour as in so called "Madness of King George" (often referenced), but that is pretty rare. It should also only occur during the attack and then disappear completely.
The condition also causes other complications like extreme pain and in some cases bowl problems during said attack, but again these return to normal.
What exactly do you mean by "never comprehend basic things". If this carries on all the time then I'm not at all sure this AIP condition is what they've got.
It sounds like they might have some kind of psychological condition and would be worth speaking to your doctor about as they may be able to either give you things to look for, or point you to a professional in that field.
Do they realise they are becoming agressive, or do they seem oblivious to it...?
http://www.bbc.co.uk/health/conditions/porphyr ia1.shtml
Gives a bit of detail on symtoms.
It's hard to say from here, but I just hope they aren't like an ex-partner of one of my friends who is just a really nasty guy by nature. Karma caught up with him eventually however...