Some common diseases include arthritis, osteoporosis, and leukemia.This website includes these and goes over more, but for now, let’s focus on the ones included above. Arthritis is an inflammatory condition that attacks the joints of the body and is characterized by joint pain, swelling, and stiffness. Osteoporosis occurs when bones become brittle and weak due to loss of bone tissue. Leukemia is a form of cancer, originating from the bone marrow and affects the lymphatic system..