Overview
Disorders of ornithine or proline metabolism are a group of rare inherited conditions that affect how the body breaks down and uses two amino acids — ornithine and proline. Amino acids are the building blocks of proteins, and when the enzymes that process them do not work properly, harmful substances can build up in the blood, urine, and tissues. This group includes several distinct conditions, such as Gyrate Atrophy of the Choroid and Retina (caused by a deficiency of the enzyme OAT), Hyperornithinemia-Hyperammonemia-Homocitrullinuria (HHH syndrome), and disorders of proline metabolism including Hyperprolinemia Type I and Type II, as well as Prolidase Deficiency. These conditions can affect many parts of the body depending on which specific disorder is present. Common areas of impact include the eyes, brain, muscles, kidneys, and skin. For example, Gyrate Atrophy causes progressive vision loss, while HHH syndrome can lead to high ammonia levels in the blood that affect brain function. Proline disorders may cause intellectual disability, seizures, or skin ulcers. Treatment varies by condition but often includes special low-protein diets, vitamin supplements (such as vitamin B6 for some forms), and medications to reduce ammonia levels. While there is currently no cure for most of these disorders, early diagnosis and careful management can significantly slow disease progression and improve quality of life.
Key symptoms:
Progressive vision loss or tunnel visionNight blindnessIntellectual disability or learning difficultiesSeizures or epilepsyHigh ammonia levels in the blood (hyperammonemia)Confusion or altered mental state, especially after eating proteinMuscle weaknessSkin ulcers or sores that are slow to healRecurrent infectionsShort stature or poor growthBehavioral problems or psychiatric symptomsKidney problemsFatigue and low energy
Autosomal recessive
Passed on when both parents carry the same gene change; often skips generations
Variable
Can begin at different ages, from infancy through adulthood
Treatments
No FDA-approved treatments are currently listed for Disorder of ornithine or proline metabolism.
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Specialists
View all specialists →No specialists are currently listed for Disorder of ornithine or proline metabolism.
Treatment Centers
8 centersBaylor College of Medicine Rare Disease Center ↗
Baylor College of Medicine
📍 Houston, TX
🏥 NORDStanford Medicine Rare Disease Center ↗
Stanford Medicine
📍 Stanford, CA
🔬 UDNNIH Clinical Center Undiagnosed Diseases Program ↗
National Institutes of Health
📍 Bethesda, MD
🔬 UDNUCLA UDN Clinical Site ↗
UCLA Health
📍 Los Angeles, CA
🔬 UDNBaylor College of Medicine UDN Clinical Site ↗
Baylor College of Medicine
📍 Houston, TX
🔬 UDNHarvard/MGH UDN Clinical Site ↗
Massachusetts General Hospital
📍 Boston, MA
🏥 NORDMayo Clinic Center for Individualized Medicine ↗
Mayo Clinic
📍 Rochester, MN
👤 Mayo Clinic Center for Individualized Medicine
🏥 NORDUCLA Rare Disease Day Program ↗
UCLA Health
📍 Los Angeles, CA
Travel Grants
No travel grants are currently matched to Disorder of ornithine or proline metabolism.
Community
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Caregiver Resources
NORD Caregiver Resources
Support, advocacy, and financial assistance for caregivers of rare disease patients.
Mental Health Support
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Family & Caregiver Grants
Financial assistance programs specifically for caregivers of rare disease patients.
Social Security Disability
Learn how rare disease patients may qualify for SSDI/SSI benefits.
Questions for your doctor
Bring these to your next appointment
- Q1.Which specific disorder within this group do I have, and what does that mean for my treatment and outlook?,Do I need genetic testing, and should my family members be tested as well?,What dietary changes do I need to make, and can I be referred to a metabolic dietitian?,Are there any clinical trials or new treatments I should know about?,How often do I need monitoring tests, and what should I watch for at home as a warning sign?,What should I do in an emergency, such as if I develop confusion or seizures?,Are there patient support groups or resources that can help me connect with others who have this condition?
Common questions about Disorder of ornithine or proline metabolism
What is Disorder of ornithine or proline metabolism?
Disorders of ornithine or proline metabolism are a group of rare inherited conditions that affect how the body breaks down and uses two amino acids — ornithine and proline. Amino acids are the building blocks of proteins, and when the enzymes that process them do not work properly, harmful substances can build up in the blood, urine, and tissues. This group includes several distinct conditions, such as Gyrate Atrophy of the Choroid and Retina (caused by a deficiency of the enzyme OAT), Hyperornithinemia-Hyperammonemia-Homocitrullinuria (HHH syndrome), and disorders of proline metabolism includ
How is Disorder of ornithine or proline metabolism inherited?
Disorder of ornithine or proline metabolism follows a autosomal recessive inheritance pattern. Genetic counseling can help families understand recurrence risk and testing options.