The diagnosis of mitochondrial disorders underwent a tremendous change towards the Next generation sequencing (NGS) methods in recent years. However, functional validations of the NGS findings are still crucial on the way to design suitable treatment options. The explanation of phenotypic-genotypic correlation led to a suggestion of rational treatments based on the experimental observations and enzymatic function of studied enzymes (TXN2 and FLAD1). Those observations will help to initiate the therapy early enough in any potential future patients carrying malfunction in either of the proteins.