The inner membrane of the mitochondria is the major site of the ATP production via oxidative phosphorylation (OXPHOS). There are five multi-protein subunit complexes that create the essential building blocks of the OXPHOS system.^1-3 (Table 1) Deficiencies of these complexes lead to OXPHOS disorders, which result in a vast array of clinical manifestations.³ Clinical diseases are no longer confined to rare neuromuscular disorders with ragged-red fibers and structurally abnormal mitochondria (e.g. Leigh syndrome, MERRF, MELAS etc.)⁴

The catalogue of pediatric and adult phenotypes is expanding at a rate suggesting that OXPHOS diseases may be one of the most commonly encountered classes of degenerative diseases.^3,4 Neuroradiologic examination is important in patients with suspected OXPHOS disease. Symptomatic of asymptomatic lesions suggesting the presence of mitochondrial OXPHOS disease can be revealed by MRI/MRS evaluation. ^5-11

Table 1: Mitochondrial OXPHOS system

Glutamate, pyruvate b-hydroxybutyrate Succinate Complex I Complex II Ubiquinone Complex III Complex IV Complex V ADP+Pi ATP

The Molecular Genetics Laboratory at Scottish Rite is a referral center for pediatric patients with suspected mitochondrial OXPHOS disease. Routine work-up of these patients includes MRI and MRS. A retrospective review of 192 pediatric patients with OXPHOS disease was performed in an attempt to categorize the MRI abnormalities that can be observed. The results of the review revealed various patterns of disease summarized in Tables 2 and 3. Single voxal MRS was prospectively performed in 52 patients. The findings from the MRS analysis in these patients are reported in Table 4.