The KHENERGYC Study

Inclusion criteria

• ✓. Age between 0 months and 17 years
• ✓. Genetically confirmed mitochondrial disease, of which the gene defect is known to decrease one or more oxidative phosphorylation system enzymes and who suffer from motor symptoms, based on investigator judgement
• ✓. Abnormal gross motor function and/or presence of at least one clinically significant motor symptom (hypotonia, decreased muscle strength, ataxia, dystonia, chorea and/or spasticity) based on investigator judgement
• ✓. Before enrollment in the adaptive PK phase and before randomization into the double-blind placebo-controlled phase: Gross Motor Function Measure-88 (GMFM-88) Total Score ≤96%
• ✓. Before enrollment in the adaptive PK phase and before randomization into the double-blind placebo-controlled phase: International Paediatric Mitochondrial Disease Scale IPMDS Score ≥10
• ✓. Stable disease symptoms since the previous routine control visit (consistent with a score of "stable" on the item "disease course since previous IPMDS" of the IPMDS) in the opinion of the investigator.
• ✓. Written informed (patient/parental/caregiver) consent, able and willing to comply with the study requirements of the study protocol.
• ✓. Women of childbearing potential must be willing to use highly effective contraceptive methods during the entire study, i.e. combined (estrogen and progestogen containing) oral, intravaginal or transdermal hormonal contraception associated with inhibition of ovulation; oral, injectable, or or implantable progestogen-only hormonal contraception associated with inhibition of ovulation; use of an intrauterine device; an intrauterine hormone releasing system, bilateral tubal occlusion and vasectomy of the partner. Any hormonal contraception method must be supplemented with a barrier method (preferably male condom). Vasectomised partner is considered a highly effective birth control method provided that partner is the sole sexual partner of the subject and that the vasectomised partner has received medical assessment of the surgical success. Sexual abstinence is considered a highly effective method only if defined as refraining from heterosexual intercourse during the entire period of risk associated with the study treatments. Reliability of sexual abstinence needs to be evaluated in in relation to the duration of the clinical trial and the preferred and usual lifestyle of the subject. Periodic abstinence (e.g., calendar, ovulation, symptothermal, post-ovulation methods) and withdrawal are not acceptable methods of contraception.