Participants will be asked to provide updated address and telephone information and the names of two contact persons, such as siblings or friends. Patients will be seen about once a year at the NIH Clinical Center to provide an update on their health status and donate a small blood sample (about 2 teaspoons), which will be frozen and stored. If a patient acquires a serious illness, such as cancer, his or her stored blood will be tested; another of blood or tissue sample may also be requested for further study. If a patient develops a medical problem that is thought possibly to be related to gene therapy, the illness will be investigated. The annual follow-up visits will continue indefinitely or until the patient declines to continue participation.