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Synonym(s) HHH syndrome
Triple H syndrome
Prevalence Unknown
Inheritance -
Age of onset Childhood
  • E72.4
  • C0268540
MeSH -
MedDRA -


The triple H syndrome (hyperornithinemia, hyperammonemia, and homocitrullinuria) is a very rare autosomal recessive genetic disease due to defective transportation of ornithine into the mitochondria. This causes a functional deficiency in ornithine transcarbamylase and ornithine aminotransferase. Onset may be neonatal, infantile or juvenile (until adolescence). The initial clinical signs are coma due to hyperammonemia, convulsions, and hypotonia. When left untreated, triple H syndrome may result in mental deficiencies, spastic hemiplegia, and anomalies in the white matter. In some moderate adult cases, hyperammonemia and liver disorders are noted but there are no neurological signs. Chromatography of plasmatic and urinary aminoacids and plasmatic ammonemia show the characteristic association of hyperammonemia, urinary excretion of homocitrulline (derived from lysine), plasmatic hyperornithinemia, and elevated excretion of orotic acid. Diagnosis is confirmed by the in vitro demonstration of impaired transportation of ornithine into the mitochondria. This technique is also applicable for prenatal diagnosis. Patients are advised to follow a diet with limited protein intake and receive arginine and citrulline supplements. Some patients respond to ornithine supplementation, although it seems contradictory.

Expert reviewer(s)

  • Pr Jean-Marie SAUDUBRAY

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Detailed information

Emergency guidelines
  • EN (2012,pdf)
Clinical practice guidelines
  • EN (2012)
Article for general public
  • NL (2011,pdf)
  • ES (2011,pdf)
  • FR (2011,pdf)
  • IT (2011,pdf)
  • PT (2011,pdf)
  • DE (2011,pdf)
  • EN (2011,pdf)
Clinical genetics review
  • EN (2012)
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