Gyrate atrophy is a rare cause of retinal degeneration known for several decades. Its cause was traced to an enzyme deficiency in the early 1970s and the responsible mutant gene identified about 1992. It occurs worldwide but most cases have been identified in Finland
This is a degenerative disorder of the retina caused by high levels of an amino acid known as ornithine, the result of a defective enzyme that normally breaks it down. Exactly how and why the retina is damaged remains unknown.
The first symptoms are nightblindness which may begin in late childhood although changes in the retina can be seen as early as five years of age. Extreme nearsightedness is common. Vision is usually good throughout childhood but by the third and fourth decades of life it is often 20/200, the equivalent of legal blindness. The retina deteriorates from the periphery to the center causing a progressive narrowing of the field of vision. Some individuals maintain a small central field of view into late adulthood. Cataracts occur early and may require surgery.
Various treatments have been tried in an attempt to reduce the circulating level of ornithine. Dietary restrictions of protein, especially the amino acid arginine, can lower the protein level and results so far suggest that this can slow the progression of disease.
The only symptoms of this condition are due to changes in the eye.
High levels of ornithine result from a defect in an enzyme that normally breaks it down. Gyrate atrophy is an autosomal recessive disease that requires the presence of two defective genes, one inherited from each parent, which code for this gene. Since one copy of the normal gene makes enough enzyme to handle the breakdown of ornithine, carrier parents do not have gyrate atrophy but if both parents have one copy, there is a 25 per cent chance that each of their children will inherit the two defective copies. Many mutations in this gene have been identified.
Gyrate atrophy is diagnosed by finding high levels of ornithine in the blood and urine. However, an eye doctor can detect the unique changes inside the eye and arrive at a presumptive diagnosis.
The retinal degeneration is progressive and vision generally becomes slowly worse. Early evidence suggests that dietary modifications such as protein and ornithine restriction can slow the progression but more documentation is needed. Low vision counseling and aids can be a significant help.
If cataracts progress so that they interfere with clear images, surgical removal can improve vision at least temporarily. Night blindness can be a significant problem and usually worsens with age.