Decreased transport of ornithine across the inner mitochondrial membrane as a cause of hyperornithinaemia.

Hyperornithinaemia due to a transport of ornithine across the inner mitochondrial membrane was demonstrated in three patients by measuring ornithine uptake by fibroblast mitochondria. Particulate compartments and soluble cytoplasm of fibroblasts were separated by a slight modification of the digitonin method of Zuurendonk and Tager. Patients' fibroblast pellet fraction contained significantly less radioactivity than control fibroblast pellet fraction after incubation of fibroblasts with [14C]-ornithine. Since neither of the patients was deficient in ornithine-delta-oxoacid aminotransferase, we concluded that in these hyperornithinaemia patients a defect exists for transport of ornithine across the inner mitochondrial membrane. The exact nature of this transport defect remains to be elucidated.