 Patients who have been identified as having MNGIE by genetic testing andor reduced thymidine phosphorylase levels will be considered for this study. The study team physician will evaluate the condition of the patient and determine if they are eligible. An HLA matched donor is necessary for transplantation. If a suitable donor is found the transplant process can proceed. The patient receives immunosuppressive therapy 1 week in the hospital with subsequent IV transfer of stem cells from the donor. The patient remains in the hospital for approximately 1 month to monitor the transplant. The patient is required to attend research visits at days 0, 100, 6m, 18m and 24 m. 