Patients will undergo screening history, physical examination, and clinical laboratory evaluation, usually in the outpatient department. Imaging studies and other procedures may be performed when clinically indicated. Where appropriate, we will ask probands to obtain permission from family members to be contacted. We will collect blood samples from consenting affected individuals and, in some cases, unaffected family members, extract DNA, and perform molecular genetic analyses. For cellular and biochemical studies, we will obtain blood samples and possibly salivary samples from patients, selected unaffected family members, and unrelated controls. In some cases adult patients may be asked to interrupt treatment temporarily to obtain additional blood samples.