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HHH syndrome

Ammonia is detoxified through its conversion to urea by the enzymes in the small boxes. Ornithine transporter 1 (ORNT1) catalyzes the transport of ornithine from the cytosol into the mitochondrion and in return the transport of citrulline from the mitochondrion into the cytosol. Deficiency of ORNT1 (highlighted in red) causes hyperornithinemia, hyperammonemia, and homocitrullinuria as well as normal to low normal plasma lysine, citrulline, and arginine levels. Urinary orotic acid might be increased. NAGS, N-acetylglutamate synthase; CPS1, Carbamyl phosphate synthetase 1; OTC, Ornithine transcarbamylase; ASS Argininosuccinate synthetase; ASL, Argininosuccinate lyase; ARG1, Arginase 1. (Contributed by Dr. Georg Hoffmann.)

Associated Disorders

  • Ataxia
  • Cerebral palsy
  • Congenital hyperammonemia
  • Hereditary spastic paraplegia
  • Mental retardation
  • Reye syndrome
  • Valproate sensitivity