RP103

The primary analysis of WBC cystine was performed using the natural log transformed WBC cystine level; the log transformation is a normalizing transformation. For each participant, the difference between the morning and corresponding non-morning log WBC cystine value (non-morning minus morning) at each monthly visit during the Cystagon® phase (Months 1, 2, and 3) was computed and these differences were averaged. The average difference between morning and non-morning log WBC cystine value was similarly computed for each participant during the RP103 phase (Months 5, 6, and 7). The primary analysis compared within-subject pairs (Cystagon® phase paired with RP103 phase) of non-morning minus morning average differences of log WBC cystine level.

Blood samples were taken 30 minutes after the morning RP103 dose at each study visit to determine White Blood Cell (WBC) cystine concentration. WBC cystine concentrations were determined using liquid chromatography.

Drug-related adverse events (AEs) are AEs the investigator assessed as having relation to drug of 'possibly', 'probably' or 'definitely'. The severity of AEs was categorized according to the Common Terminology Criteria for Adverse Events (CTCAE), Version 3.0 as follows: * Mild (Grade 1): experience is minor and does not cause significant discomfort to subject or change in activities of daily living (ADL); subject is aware of symptoms but symptoms are easily tolerated; * Moderate (Grade 2): experience is an inconvenience or concern to the subject and causes interference with ADL, but the subject is able to continue with ADL. * Severe (Grade 3): experience significantly interferes with ADL and the subject is incapacitated and/or unable to continue with ADL * Life-threatening (Grade 4): experience that, in the view of the Investigator, places the subject at immediate risk of death from the event as it occurred.

The NPMDS evaluates the progression of mitochondrial disease in pediatric patients in 4 domains: I - Current Function (vision, hearing, communication, feeding, and mobility) with scores ranging from 0 to 21; II -System Specific Involvement (seizures, encephalopathy, bleeding diathesis or coagulation defects, gastrointestinal, endocrine, respiratory, cardiovascular, renal, liver, and blood) with scores ranging from 0 to 30. III - Current Clinical Assessment (growth and development over past 6 months, vision, strabismus and eye movement, myopathy, ataxia, pyramidal, extrapyramidal, and neuropathy) with scores ranging from 0 to 28; and IV - Quality of Life with scores ranging from 0 to 25. For sections I-III, higher scores reflect more severe disease. For Section IV, a higher score reflects a lower quality of life.