GTR Home > Conditions/Phenotypes > Hyperornithinemia-hyperammonemia-homocitrullinuria syndrome

Disease characteristics

Excerpted from the GeneReview: Hyperornithinemia-Hyperammonemia-Homocitrullinuria Syndrome
Hyperornithinemia-hyperammonemia-homocitrullinuria (HHH) syndrome is characterized by variable clinical presentation and age of onset. Neonatal onset (~12% of affected individuals). Infants are normal for the first 24-48 hours followed by onset of symptoms related to hyperammonemia (poor feeding, vomiting, lethargy, low temperature, rapid breathing). Information on long-term outcome is limited. Infancy, childhood, and adult presentation (~88%). Affected individuals may present with: Chronic neurocognitive deficits (including developmental delay, ataxia, spasticity, learning disabilities, cognitive deficits and/or unexplained seizures); Acute encephalopathy secondary to hyperammonemic crisis precipitated by a variety of factors; and Chronic liver dysfunction (unexplained elevation of liver transaminases with or without mild coagulopathy, with or without mild hyperammonemia and protein intolerance). Neurologic findings and cognitive abilities can continue to deteriorate despite early metabolic control that prevents hyperammonemia.

Available tests

40 tests are in the database for this condition. Compare labs offering these tests.

Check Associated genes for additional relevant tests.

Associated genes

  • Also known as: RP11-346L13.4, D13S327, HHH, ORC1, ORNT1, SLC25A15
    Summary: solute carrier family 25 (mitochondrial carrier; ornithine transporter) member 15

Clinical features

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  • Hyperreflexia
  • Poor coordination
  • Episodic vomiting
  • Protein avoidance
  • Intellectual disability
  • Failure to thrive
  • Chorioretinal atrophy
  • Decreased nerve conduction velocity
  • Lethargy
  • Coma
  • Global developmental delay
  • Specific learning disability
  • Decreased liver function
  • Hyperammonemia
  • Morphological abnormality of the pyramidal tract
  • Cerebral cortical atrophy
  • Generalized myoclonic seizures
  • Clonus
  • Hepatomegaly
  • Spastic paraparesis
  • Impaired vibratory sensation
  • Acute encephalopathy
  • Hypopigmentation of the fundus
  • Hyperornithinemia
  • Acute hepatitis
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