Study subjects will continue the triheptanoin-supplemented diet for a period of 12 months and then be able to continue into an indefinite extension phase in this compassionate use study. Laboratory evaluations will take place at two, six, and twelve months, as well as every 12 months in the extension phase. Laboratory tests may be completed at a local lab and the results forwarded to the PI for review between visits in Pittsburgh. Patients will monitor their weight at home on a monthly basis. Interim metabolic evaluations will be arranged as needed on a clinical basis with the study PI or the subject's home metabolic physician. Following the initial 12 months of the protocol, subjects will be placed on a continuing schedule for maintenance of triheptanoin therapy with a yearly follow up visit for an undeterminable period of time. Echocardiograms must be completed on an annual basis and sent to the study PI to review.