Conditions Hyperornithine with Gyrate Deficiency
Hyperornithine with gyrate deficiency (Hyper ORN) is an inherited condition that results in progressive vision loss. It is considered an amino acid condition because individuals with Hyper ORN are unable to breakdown and process a certain amino acid (building blocks of protein) called ornithine. This causes harmful levels of ornithine to build up in the body, leading to a variety of problems affecting the eyes. In some cases, detecting Hyper ORN early and beginning proper treatment may help prevent or delay some of the severe health outcomes associated with the condition.
Amino Acid Disorders
Hyperornithine with gyrate deficiency is a rare condition with only about 200 confirmed cases worldwide. It appears to be most common in individuals of Finnish descent.
Also known as
- Hyper ORN
- Hyperornithinemia with Gyrate Atrophy of Choroid and Retina
- Gyrate Atrophy
- Ornithine Aminotransferase Deficiency
- Ornithine Keto Acid Aminotransferase Deficiency
- Ornithine-Delta-Aminotransferase Deficiency
- Gyrate Atrophy of Choroid and Retina
Your baby’s doctor may ask you if your baby is showing any of the signs of hyperornithine with gyrate deficiency (see Early Signs below). If your baby has certain signs, your baby’s doctor may suggest starting immediate treatment.
If your baby’s newborn screening result for hyperornithine with gyrate deficiency (Hyper ORN) was out of the normal range, your baby’s doctor or the state screening program will contact you to arrange for your child to have additional testing. It is important to remember that an out-of-range screening result does not necessarily mean that your child has the condition. An out-of-range result may occur because the initial blood sample was too small or the test was performed too early. However, as a few babies do have the condition, it is very important that you go to your follow-up appointment for a confirmatory test. Because the harmful effects of untreated Hyper ORN can occur soon after birth, follow-up testing must be completed as soon as possible to determine whether or not your baby has the condition.
Follow-up testing will involve checking your baby’s urine or blood for signs of Hyper ORN. When a child has an amino acid condition, harmful amounts of certain substances build up in the body and enzymes that help the body breakdown specific amino acids are either missing or have reduced activity. Measuring the amounts of these substances in your baby’s body can help doctors determine if your baby has a condition. High amounts of the amino acid, ornithine, in the blood and urine or deficient activity of the enzyme, ornithine aminotransferase, in the blood might indicate that your baby has Hyper ORN. For a definitive diagnosis, your doctor may need to order genetic testing or study the enzyme activity in a small sample of your baby’s skin.
About Hyperornithine with Gyrate Deficiency
Individuals with hyperornithine gyrate deficiency (Hyper ORN) usually do not develop signs or symptoms of the condition until later in childhood or even into adulthood. These early signs include:
- Inability to see at night or in poor lighting (night blindness)
- Trouble seeing objects at a distance (myopia)
- Loss of peripheral (side) vision
- Narrowing field of vision (tunnel vision)
Rarely, newborns with Hyper ORN may also experience the following signs:
- Poor feeding
- Mild intellectual disability
- Muscle weakness
If your baby shows any of these signs, be sure to contact your baby’s health care provider immediately.
Your baby may need to be on a low-protein diet to avoid the amino acids that his or her body cannot break down. A nutritionist or dietician can help you monitor your baby’s calorie intake and plan a diet that will provide the nutrients he or she needs.
Supplements and Medications:
Your baby’s doctor may also prescribe vitamin B6 (pyridoxine) supplements. In some babies with hyperornithine gyrate deficiency (Hyper ORN), this treatment helps reduce the levels of ornithine in the blood, increase activity of the ornithine aminotransferase enzyme and prevent or slow vision loss.
In some cases, detecting hyperornithine gyrate deficiency (Hyper ORN) early and beginning proper treatment may help prevent or delay vision loss and other health problems associated with the condition. This is why newborn screening for Hyper ORN is so important.
Unfortunately, even with treatment, many individuals with Hyper ORN will have problems with vision, often leading to blindness. Some individuals may also experience learning disabilities and muscle weakness.
When we eat food, enzymes help break it down. Some enzymes are responsible for breaking down proteins into their building blocks, called amino acids. Other enzymes break down these amino acids into smaller components to be used by our bodies. The enzyme, ornithine aminotransferase (OAT), specifically, helps our bodies break down and process the amino acid, ornithine.
If your baby has hyperornithine gyrate deficiency (Hyper ORN), his or her body is missing or making non-working copies of the OAT enzyme. When this enzyme is not working, ornithine cannot be properly broken down. This causes high levels of ornithine to build up throughout the body. It is currently unclear how high levels of ornithine lead to the variety of signs and symptoms associated with Hyper ORN.
Hyper ORN is an autosomal-recessive genetic condition. This means that a child must inherit two copies of the non-working gene for the OAT enzyme, one from each parent, in order to have the condition. The parents of a child with an autosomal recessive condition each carry one copy of the non-working gene, but they typically do not show signs and symptoms of the condition. While having a child with Hyper ORN is rare, when both parents are carriers, they can have more than one child with the condition. Learn more about autosomal recessive inheritance.
Support for Hyperornithine with Gyrate Deficiency
Support groups can help connect families who have a child or other family member affected with hyperornithine with gyrate deficiency with a supportive community of people who have experience and expertise in living with the condition. These organizations offer resources for families, affected individuals, health care providers, and advocates. Many organizations such as the American Foundation for the Blind specialize in support for individuals with vision loss. Other organizations specialize in supporting families or individuals affected by metabolic disorders.
Work with your baby’s health care provider to determine the next steps for your baby’s care. Your baby’s doctor may help you coordinate care with a physician that specializes in metabolism, a dietician who can help plan your child’s specialized diet, and other medical resources in your community.
Because hyperornithine with gyrate deficiency is a genetic condition, you may want to talk with a genetics specialist. A genetic counselor or geneticist can help you understand the causes of the condition, discuss genetic testing for defects in the OAT gene, and understand what this diagnosis means for other family members and future pregnancies. Speak with your baby’s doctor about getting a referral. The Clinic Services Search Engine offered by the American College of Medical Genetics and Genomics (ACMG) and the Find a Genetic Counselor tool on the National Society of Genetic Counselors (NSGC) website are two good resources for you or your baby's health care provider to use to identify local specialists.
References & Sources
Visit OMIM to search its online catalog of human genes and disorders
Visit Genetic and Rare Diseases Information Center (GARD) for more condition information
Visit MedlinePlus Genetics for more condition information
Visit the Newborn Screening Coding and Terminology Guide by the U.S. Library of Medicine for condition information
Ohkubo Y, Ueta A, Ito T, Sumi S, Yamada M, Ozawa K, Togari H. Vitamin B6-responsive ornithine aminotransferase deficiency with a novel mutation G237D. Tohoku J Exp Med. 2005 Apr; 205(4):335-42.