Urea Cycle Related Amino Acids Measured in Dried Bloodspots Enable Long-Term In Vivo Monitoring and Therapeutic Adjustment

Background: Dried bloodspots are easy to collect and to transport to assess various metabolites, such as amino acids. Dried bloodspots are routinely used for diagnosis and monitoring of some inherited metabolic diseases. Methods: Measurement of amino acids from dried blood spots by liquid chromatography-tandem mass spectrometry. Results: We describe a novel rapid method to measure underivatised urea cycle related amino acids. Application of this method enabled accurate monitoring of these amino acids to assess the efficacy of therapies in argininosuccinate lyase deficient mice and monitoring of these metabolites in patients with urea cycle defects. Conclusion: Measuring urea cycle related amino acids in urea cycle defects from dried blood spots is a reliable tool in animal research and will be of benefit in the clinic, facilitating optimisation of protein-restricted diet and preventing amino acid deprivation.

HHH Syndrome

Hyperornithinemia-hyperammonemia-homocitrullinuria (HHH) syndrome is an autosomal recessive disorder of the urea cycle characterized by impaired transport of ornithine across the inner mitochondrial membrane. As seen in other urea cycle defects, in the acute phase the disease is characterized by intermittent episodes of hyperammonemia accompanied by vomiting, lethargy, and coma, with or without signs of acute liver failure. The disease course is characterized by a pyramidal tract dysfunction associated with myoclonic seizures and cerebellar symptoms. Most patients reaching adulthood manifest variable degrees of cognitive impairment and abnormal behavior. Long-term treatment consists of a low-protein diet supplemented with citrulline, arginine, or ornithine. Protein restriction may be combined with sodium benzoate. If plasma creatine levels are low, creatine supplementation should be instituted. Acute treatment is similar to other urea cycle defects.