People with diagnosed or undiagnosed conditions may participate in this screening protocol. They will undergo procedures that may include questionnaires, a physical examination, routine laboratory tests, and diagnostic imaging or radiological studies. Eligibility screening will be limited to three visits within 12 months of entry into the protocol. If an appropriate study is not found by the end of this time, the candidate's participation in the screening program will terminate. No experimental treatments are offered under the screening protocol.