Rare diseases · Sign or symptom
Hyperammonemia
High blood ammonia levels
HP:0001987
What it means
An increased concentration of ammonia in the blood.
Rare diseases that can present with this44
Very common80–99%
11- 3-hydroxy-3-methylglutaric aciduria
- Argininosuccinic aciduria
- Carbamoyl-phosphate synthetase 1 deficiency
- Carnitine-acylcarnitine translocase deficiency
- Citrullinemia type I
- Hyperammonemia due to N-acetylglutamate synthase deficiency
- Hyperornithinemia-hyperammonemia-homocitrullinuria syndrome
- Ornithine transcarbamylase deficiency
- Propionic acidemia
- TMEM70-related mitochondrial encephalo-cardio-myopathy
- Vitamin B12-unresponsive methylmalonic acidemia type mut-
Common30–79%
16- 3-methylcrotonyl-CoA carboxylase deficiency
- Acute liver failure
- Acyl-CoA dehydrogenase 9 deficiency
- Argininemia
- Beta-ketothiolase deficiency
- Biotinidase deficiency
- Holocarboxylase synthetase deficiency
- Hyperlysinemia
- Isolated ATP synthase deficiency
- Isovaleric acidemia
- Lysinuric protein intolerance
- Medium chain acyl-CoA dehydrogenase deficiency
- Neonatal intrahepatic cholestasis due to citrin deficiency
- Pyruvate carboxylase deficiency
- Recurrent metabolic encephalomyopathic crises-rhabdomyolysis-cardiac arrhythmia-intellectual disability syndrome
- Vitamin B12-responsive methylmalonic acidemia
Sometimes5–29%
12- Carnitine palmitoyl transferase II deficiency, neonatal form
- HSD10 disease, infantile type
- Hyperinsulinism due to short chain 3-hydroxylacyl-CoA dehydrogenase deficiency
- MEGDEL syndrome
- Methylmalonic acidemia with homocystinuria, type cblC
- Multiple acyl-CoA dehydrogenase deficiency
- Pyruvate dehydrogenase E3 deficiency
- Rett syndrome
and 4 more in this range
The range is how often this sign appears among people diagnosed with each disease — it is not a probability of having any of them. Many of these signs also occur in common, non-rare conditions. A sign on this page is a conversation to have with a clinician, not a conclusion.
Part of the broader category
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Start free with EleplanThis page uses the Human Phenotype Ontology (2026-06-23) — Human Phenotype Ontology Consortium, hpo.jax.org. Disease associations from Orphanet (INSERM), CC BY 4.0. Content is educational and is not medical advice.