Any disease can affect the organ system because it invades the body and alters the way things work. Different diseases will affect different organs. This diseases can be caused by genetics, bacteria, poor nutrition, viruses, parasites and fungi. Diseases will damage or change the way the organ system works, causing harm to the body. An example of this is Sarcoidosis, this disease usually starts in the lungs and can also affect other organs. When many granulomas form in an organ, they can affect how the organ works.