Role of plasma amino acids and urinary organic acids in diagnosis of mitochondrial diseases in children

Pediatr Neurol. 2014 Dec;51(6):820-5. doi: 10.1016/j.pediatrneurol.2014.08.009. Epub 2014 Aug 27.


Background: 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 amino acids, and urinary organic acids.

Methods: Twenty patients with symptoms and signs suggestive of MD were further evaluated by quantitative plasma amino acids and urinary organic acids assay and neuroimaging.

Results: Plasma amino acid results revealed elevation of alanine in 11, 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%). Upon enrollment our patients scored as possible MD according to the MD scoring system. At the end of the study, five patients still scored as possible MD, eight patients as probable MD, and seven patients as definite MD. All patients with definite MD had elevated serum lactate. In three patients, elevated urinary lactate was the only abnormality. Alanine was elevated in all patients with definite MD, whereas proline was elevated in only one. Magnetic resonance imaging of the brain showed atrophic changes in one patient and bilateral basal ganglia hyperintensity in another.

Conclusion: Urinary organic acids and quantitative plasma amino acids can help in the diagnosis of MD, especially when the economic burden and absence of specialized centers limits the diagnosis.

Keywords: mitochondrial disease; plasma amino acids; urinary organic acids.

MeSH terms

  • Amino Acids / blood*
  • Biomarkers* / blood
  • Biomarkers* / urine
  • Carboxylic Acids / urine*
  • Child
  • Child, Preschool
  • Female
  • Humans
  • Infant
  • Male
  • Mitochondrial Diseases / blood
  • Mitochondrial Diseases / diagnosis*
  • Mitochondrial Diseases / urine


  • Amino Acids
  • Biomarkers
  • Carboxylic Acids