Cavernous malformations can occur anywhere in the body, but usually only produce symptoms when they are found in the brain and spinal cord. Some people with CCM – experts estimate 25 percent -- will never experience any related medical problems. Others will have serious symptoms such as seizures (most commonly), headaches, paralysis, hearing or vision changes, and bleeding in the brain (cerebral hemorrhage). There are familial (inherited) and sporadic (occurring for no clear reason) cases of CCM. Researchers have discovered three different genes associated with CCM. Studies are currently underway to understand the relationship between the mutations of each of these genes and their corresponding symptoms.