Hyperornithinemia-hyperammonemia-homocitrullinuria syndrome

What is Hyperornithinemia-hyperammonemia-homocitrullinuria syndrome?

A rare, genetic disorder of urea cycle metabolism characterized by either a neonatal-onset with manifestations of lethargy, poor feeding, vomiting and tachypnea or, more commonly, presentations in infancy, childhood or adulthood with chronic neurocognitive deficits, acute encephalopathy and/or coagulation defects or other chronic liver dysfunction.

Other condition names

  • HHH syndrome
  • ORNT1 deficiency
  • Ornithine carrier deficiency
  • Ornithine translocase deficiency
  • Triple H syndrome

Inheritance type

Autosomal recessive


  • Worldwide: Unknown
  • Europe: <1 in 1,000 000

Age of Onset

  • Adolescent
  • Adult
  • Childhood
  • Infancy
  • Neonatal
Orphadata: Free access data from Orphanet. © INSERM 1999. Available on "https://www.orphadata.com". Data version 1.3.16 / 4.1.7.