The Project Genom forum has a new developer post that lays out the details on character progression in the game so far. Characters have a whopping twelve areas in which progression occurs, each with six skills and even more nodes. Additionally, there are six character organism systems that can be upgraded: Cardiovascular, Musculoskeletal, Respiratory, Nervous, Immune and Digestive systems are all eligible for progression to strengthen characters.
While traveling around the world, a character may get infected with a disease or otherwise damage any of the organs. Once an organ is infected, all features related to the organ become inactive. If a character is not healing, a disease may progress and affect other organs within one system. Also, the higher the stage of a disease, the more difficult it is to find a cure. But disease is not necessarily a bad thing. If you manage to steer the progress of a disease in the right direction, the organs of your character may develop new features.
Check out the full developer diary on the Project Genom forum.