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Start free with EleplanHyperornithinemia-hyperammonemia-homocitrullinuria syndrome
ORPHA:415Disease
Also called HHH syndrome · ORNT1 deficiency · Ornithine carrier deficiency · Ornithine translocase deficiency · Triple H syndrome
What it is
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.
Key facts
- Prevalence
- <1 / 1 000 000 (Europe)
- Age of onset
- Adolescent, Adult, Childhood, Infancy, Neonatal
- Inheritance
- Autosomal recessive
- Classified as
- Disease
Prevalence figures describe populations, not individuals, and are often estimates from a single study. Where the figure is an incidence or a birth prevalence, it says so.
Signs and symptoms
Very common80–99%
6Common30–79%
24- Abnormal pyramidal sign
- Acute encephalopathy
- Cerebral cortical atrophy
- Clonus
- Confusion
- Decreased liver function
- Elevated circulating hepatic transaminase concentration
- Episodic vomiting
- Failure to thrive
- Feeding difficulties
- Generalized hypotonia
- Hepatitis
- Hepatomegaly
- Impaired vibratory sensation
- Intellectual disability
- Lethargy
- Oroticaciduria
- Poor coordination
- Progressive cerebellar ataxia
- Protein avoidance
- Spastic paraplegia
- Specific learning disability
- Speech apraxia
- Tachypnea
Sometimes5–29%
7These ranges are how often a sign appears across everyone diagnosed, not a prediction for one person — most people have some of these and not others. Orphanet also records findings that are specifically absent in this disease; those are in the data but not listed here.
Gene
ICD-10 codes
ICD-10 has no distinct code for most rare diseases, so many are filed under the nearest available one. A shared code identifies the group, not this disease — the ORPHAcode above is what identifies it.
Related health topics
Reached through the ICD-10 categories this disease is filed under, so these describe the broader group rather than this disease specifically.
Cross-references
Orphadata Science: Free access data from Orphanet. © INSERM 1999. Data version 2026-06-23. Available under CC BY 4.0. This is a reference, not medical advice.
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