This was a movie originally rented on VHS in Germany in the late 80's. A typical case of someone putting the wrong video in a case and then someone - here, my family - getting a completely different movie than expected.

* The movie was fully animated/hand drawn. No live action and no (noticeable) rotoscoping.
* I'm not 100% sure about the origin, but most likely Japan with a complete/full German dub. Characters had slightly exaggerated body shapes.
* The movie might have started with a boy trapped in some kind of futuristic city or space station. This might be me confusing things, though.
* Later in the movie the protagonist runs around some kind of ramp or crater.
* **Most notable/memorable detail:** They're talking about some people being sick or influenced, showing this by transforming them. In a rather visual way, a human is transformed into what might have been an Orangutan (or heavily inspired by one).
* I don't remember anything after this, since it was probably a bit too much for me - combined with my father's note on this movie "being total idiocy".
* This might have been *Space Firebird 2772* (1980), although I can't find any references to the transformation.