What are the other Names for this Condition? (Also known as/Synonyms)

• Gyrate Atrophy
• Hyperornithinemia with Gyrate Atrophy of Choroid and Retina (HOGA)
• Ornithine Aminotransferase Deficiency Disorder

What is Gyrate Atrophy of Choroid and Retina? (Definition/Background Information)

• Gyrate Atrophy of Choroid and Retina (or Gyrate Atrophy) is a rare, autosomal recessive disorder causing degeneration of the choroid and retina of eye. It is a congenital condition that presents signs and symptoms in newborns and infants
• The signs and symptoms of Gyrate Atrophy may affect only the eye or the entire body (systemic). It may include tunnel vision, night blindness, and muscular atrophy on some individuals
• Gyrate Atrophy is classified into 2 subtypes based upon whether the affected individual responds to vitamin B6 (pyridoxine) therapy:
  • Those who respond are classified as one type (vitamin B6 responders), which occurs in a minority of cases. These individuals have slower progression of signs and symptoms, leading to a better prognosis
  • Those who do not respond are classified as another type (vitamin B6 non-responders), which occurs in a majority of cases. These individuals have rapid progression of signs and symptoms and the condition leads to a much worse prognosis
• The cause of Gyrate Atrophy of Choroid and Retina is a mutation in the OAT gene that encodes for a certain protein, which is necessary for normal energy production in the cells. Since, the condition is inherited, a positive family history is a key risk factor
• A healthcare provider can use various physical (eye) exams, blood tests, and imaging studies to diagnose Gyrate Atrophy of Choroid and Retina. The treatment for the condition includes dietary restrictions and vitamin B6 supplementation
• The prognosis of Gyrate Atrophy of Choroid and Retina depends on the severity of the signs and symptoms. Early detection and prompt treatment may yield better outcomes

Who gets Gyrate Atrophy of Choroid and Retina? (Age and Sex Distribution)

• Gyrate Atrophy of Choroid and Retina is a congenital condition and the onset of signs and symptoms may occur during early infancy (including in newborns)
• The condition affects both males and females
• Individuals of different racial and ethnic backgrounds can be affected. However, there is a higher prevalence of the disorder in the European nation of Finland (approximate prevalence is 1 in 50,000)
• Gyrate Atrophy is a very rare disorder with only 200 cases being reported worldwide. Of these, about 50 cases are from Finland alone

What are the Risk Factors for Gyrate Atrophy of Choroid and Retina? (Predisposing Factors)

• The main risk factor for Gyrate Atrophy of Choroid and Retina is a family history of the condition

It is important to note that having a risk factor does not mean that one will get the condition. A risk factor increases one's chances of getting a condition compared to an individual without the risk factors. Some risk factors are more important than others.

Also, not having a risk factor does not mean that an individual will not get the condition. It is always important to discuss the effect of risk factors with your healthcare provider.

What are the Causes of Gyrate Atrophy of Choroid and Retina? (Etiology)

Gyrate Atrophy of Choroid and Retina is a genetic disorder that is inherited in an autosomal recessive manner. It is classified as a type of choroidal dystrophy.

• It is caused by OAT gene mutation (located on chromosome 10), which is responsible for making the enzyme ornithine aminotransferase (OAT enzyme)
• The OAT enzyme helps in energy production in the cells. Because of this deficiency, there is an increased amount of ornithine in blood, causing a variety of signs and symptoms
• In Gyrate Atrophy, one mutated copy must be inherited from each parent, termed autosomal recessive trait. The parents may both be carriers (without any signs and symptoms), may both have the disorder, or one parent may be a carrier while the other has the disorder

Autosomal recessive: Autosomal recessive conditions are traits or disorders that occur when two copies of an abnormal gene have been inherited on a non-sex chromosome. If both parents have an autosomal recessive condition, there is a 100% likelihood of passing on the mutated genes to their children. If, however, only one mutant copy of the gene is inherited, the individual will be a carrier of the condition, but will not be present with any symptoms. Children born to two carriers, have a 25% chance of being homozygous dominant (unaffected), a 50% chance of being heterozygous (carrier), and a 25% chance of being homozygous recessive (affected).

What are the Signs and Symptoms of Gyrate Atrophy of Choroid and Retina?

The signs and symptoms of Gyrate Atrophy of Choroid and Retina are manifested at birth and may begin during early childhood. It may vary in severity from one child to another and is a progressive condition. The signs and symptoms may include:

• Newborn child may present with vomiting, act irritated, lethargy, poor feeding, failure to gain weight, convulsions, and loss of consciousness (including coma)
• Difficulty in night vision or dim-light vision (nyctalopia)
• Loss of vision field: The peripheral vision is gradually lost, while the central vision may remain unaffected. This is termed as tunnel vision
• Near vision or shortsightedness (myopia)
• Some individuals may have neuropathy affecting the peripheral nerves, resulting in symptoms such as numbness, tingling sensation, needle prick pain in the hands/feet
• Some individuals may have muscle atrophy resulting in decreased muscle strength
• The condition typically affects both the eyes (bilateral presentation)
• Individuals with Gyrate Atrophy can have widely varying signs and symptoms. Some may have only eye-related signs and symptoms, while others may have both eye-related and systemic signs and symptoms (affecting the whole body)
• Excess ammonia in blood may lead to additional signs and symptoms
• Normal intelligence is maintained in a majority of the individuals

How is Gyrate Atrophy of Choroid and Retina Diagnosed?

A healthcare professional may diagnose Gyrate Atrophy of Choroid and Retina using the following tests and procedures:

• Physical examination and analysis of previous medical history
• Eye examination by an eye specialist
• Fundoscopic (ophthalmoscopic) examination by an eye specialist, who examines the back part of the eye (or the fundus)
• Visual acuity test using a special and standardized test chart (Snellen chart)
• Slit-lamp examination: Examination of the eye structure using a special instrument called a slit-lamp. In this procedure, the pupils are dilated and the internal eye structure is examined
• Tonometry: Measurement of intraocular pressure or eye fluid pressure, especially to detect conditions such as glaucoma
• Fundus fluorescein angiography (FFA): In this technique, the eye blood vessels are examined using a fluorescein dye
• Fundus autofluorescence (FAF) imaging: It is a diagnostic technique to examine the fundus of the eye using a fluorescent dye
• Indocyanine green (ICG) angiography: It is used to examine the blood vessels of the choroid using a dye, called indocyanine green, particularly to study the choroid
• B-scan ultrasonography: Special ultrasound scan of the eye through a non-invasive diagnostic tool, to assess health of the eye structures
• Electroretinogram (ERG): It is a technique to measure electrical activities in the retinal cells
• Optical coherence tomography (OCT) of eye: Radiological imaging technique to visualize the eye structure
• Nerve conduction studies
• MRI scan of brain, in case of neurological presentations
• Tests to detect ornithine levels in blood, urine, cerebrospinal fluid, or aqueous humor of eye: An increased level of ornithine in the body fluids may be observed
• In newborns, testing for ornithine aminotransferase activity in a fibroblast cell or lymphoblast cell
• Blood tests that include:
  • Complete blood count (CBC) with differential
  • Erythrocyte sedimentation rate (ESR)
  • Testing for ammonia levels
  • Testing for OAT gene mutation on a blood sample: Molecular studies to detect the mutation can help confirm the diagnosis
• Muscle biopsy will help in determining the cause of atrophy

Note:

• Gyrate Atrophy is named so, because on a fundoscopic exam, the eye specialist may observe atrophy of the choroid and retina
• Many a times, Gyrate Atrophy is missed during the newborn stage, since it is not suspected. This is further complicated by the fact that ornithine levels in blood/urine are not a reliable test in newborns. Some newborns with the condition may have normal ornithine levels in blood/urine. Hence, Gyrate Atrophy may be missed in a newborn child
• A better test is to look for ornithine aminotransferase activity in a fibroblast cell or lymphoblast cell, in a newborn child

Many clinical conditions may have similar signs and symptoms. Your healthcare provider may perform additional tests to rule out other clinical conditions to arrive at a definitive diagnosis.

What are the possible Complications of Gyrate Atrophy of Choroid and Retina?

The complications of Gyrate Atrophy of Choroid and Retina may include:

• Complete retinal atrophy
• Retinal detachment: An eye condition wherein the retina gets separated from the eye structures that holds the retinal layers together
• Cataracts: When the lens of the eye becomes clouded and cause vision loss
• Rarely, the affected individuals may have some degree of intellectual disability

A gradual deterioration of vision is observed as the child grows and develops; over time, this results in severe vision impairment (by the time the individual reaches age 50 years). At this stage, the individuals may be declared ‘legally blind’.

How is Gyrate Atrophy of Choroid and Retina Treated?

Early diagnosis and treatment of Gyrate Atrophy of Choroid and Retina is important. This can help prevent complications that may cause irreversible damage to the eye, since Gyrate Atrophy is a progressive disorder. The treatment measures may include the following:

• Dietary restriction: Limiting arginine intake through proteins in the diet
• Vitamin B6 therapy (in individuals who respond) can help decrease ornithine levels in blood
• Surgery for cataract
• Rehabilitation, vocational, or occupational therapy may be provided to individuals with severe vision abnormality

The healthcare provider may recommend the best treatment options based upon each individual’s specific circumstances.

How can Gyrate Atrophy of Choroid and Retina be Prevented?

• Currently, there are no specific methods or guidelines to prevent Gyrate Atrophy of Choroid and Retina, since it is a genetic condition
• Genetic testing of the expecting parents (and related family members) and prenatal diagnosis (molecular testing of the fetus during pregnancy) may help in understanding the risks better during pregnancy
• If there is a family history of the condition, then genetic counseling will help assess risks, before planning for a child
• Active research is currently being performed to explore the possibilities for treatment and prevention of inherited and acquired genetic disorders such as Gyrate Atrophy

What is the Prognosis of Gyrate Atrophy of Choroid and Retina? (Outcomes/Resolutions)

• The prognosis of Gyrate Atrophy of Choroid and Retina depends upon the severity of the signs and symptoms, which may vary from mild to severe
• In some cases, with appropriate treatment, an excellent prognosis is achieved; intellectual development is also  normal
• In other cases, the condition is difficult to treat (only 5% respond to vitamin B6 therapy); despite dietary restrictions, some individuals have progression of signs and symptoms
• In some individuals, the prognosis is poor and Gyrate Atrophy leads to a gradual loss of complete vision by the age of around 50 years

Additional and Relevant Useful Information for Gyrate Atrophy of Choroid and Retina:

• There are 2 types of amino acids, termed essential and non-essential amino acids;  ornithine is a non-essential amino acid
• Initially, scientists had believed that Gyrate Atrophy was a subtype of choroideremia, but now they consider it a separate condition. Individuals with choroideremia have normal ornithine levels in blood. This is the main differentiating factor with respect to Gyrate Atrophy

Please visit our Eye & Vision Health Center for more physician-approved health information:

http://www.dovemed.com/health-topics/vision-center/