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Diagnostic difficulty in mitochondrial diseases (MD) results not only from the wide spectrum of symptoms and signs but also from the absence of a reliable screening or diagnostic biomarker. Aim: To investigate the likelihood of MD in patients with symptoms and signs impressive of MD through quantitative measurement of plasma aminoacids, and urinary organic. Methods: Twenty patients with symptoms and signs suggestive of MD, were further evaluated by quantitative plasma aminoacids and urinary organic acids assay and neuroimaging. Results: Plasma amino acid results revealed elevation of alanine in 11patients, of Glycine in five and proline in two patients. Abnormal urinary organic acid analysis was present in six patients; increased urinary lactate(20%), dicarboxylicaciduria(15%) and urinary ketone bodies(10%). According to MD scoring system (Wolf and Smeitink, 2002); upon enrollment our patients scored as possible MD. At end of study, five patients still scored as possible MD, eight patients were considered probable MD and seven patients as definite MD. All patients with definite MD had elevated serum lactate. Elevated urinary lactate in three patients was the only urinary organic acids abnormality in them. Plasma amino acid showed elevated alanine in all patients with definite MD, whereas proline was elevated in one. MRI brain showed atrophic changes in one patient and bilateral basal ganglia hyperintensity in another. Conclusion: Urinary organic acids and quantitative plasma amino acids essay is a useful part of the work up for MD, especially when the economic burden and absence of specialized centers limits the diagnostic ability.

Mitochondrial disease, Plasma aminoacids, Urinary organic acid