University of Iowa News Release
July 22, 2004
Photos: Top, left-- A scene as it might be viewed by a person with age-related macular degeneration, photo courtesey of National Eye Institute, National Institutes of Health; Top, right-- Normal vision, photo courtesey of National Eye Institute, National Institutes of Health; Bottom, left--Edwin Stone, M.D., Ph.D., UI professor of ophthalmology and visual sciences and a Howard Hughes Medical Institute (HHMI) investigator
Genetic Finding Has Significant Implications For Preventing Blindness
A genetic finding reported in the New England Journal of Medicine has broad implications for avoiding an impending epidemic of blindness in the United States and other developed nations.
In the July 22 issue of the journal, a University of Iowa team reports that a gene called fibulin 5 is associated with 1.7 percent of age-related macular degeneration (AMD) cases. The finding could help researchers develop preventive treatments for people affected by this particular form of AMD -- at least 100,000 in the United States alone. The discovery may also point the way to preventing vision loss in millions of people affected by the many other forms of AMD.
Macular degeneration affects nearly nine million people in the United States, according to the National Eye Institute (NEI). The disease commonly injures the center of a person's field of vision but leaves peripheral vision intact. Yellowish deposits called drusen accumulate under the retina, particularly under the central portion called the macula, which is required for reading and driving vision. As the drusen accumulate, many retinal cells that are essential for normal vision are lost.
Specifically, the finding could help researchers learn how drusen form, and it could help them develop tissue or animal models for testing preventive treatments, said Edwin Stone, M.D., Ph.D., UI professor of ophthalmology and visual sciences and a Howard Hughes Medical Institute (HHMI) investigator.
Stone authored the collaborative study, which involved colleagues in the UI Roy J. and Lucille A. Carver College of Medicine and the UI College of Engineering. Previous UI-led research had implicated a fibulin 3 gene defect in a rare, heritable form of macular degeneration.
In the current study, the team searched for variations in five other fibulin genes in people with AMD and people without the disease. The team found an altered fibulin 5 gene in seven of the 402 (1.7 percent) people with macular degeneration but not in any of the 429 controls.
"While 1.7 percent may seem insignificant, the 100,000 to 150,000 people it represents in the United States actually is a larger group of people than all those with Hodgkins disease or sickle cell anemia," Stone said.
Age-related macular degeneration is really a large group of diseases, perhaps as many as 50. Thus, it is likely that that researchers will eventually find numerous genetic clues to be involved in the various forms of this common disease.
"Previously researchers thought we might find a single gene that accounts for as much as 25 percent of all macular degeneration, but now we know we need to look for smaller signals," said Stone, who also directs the UI Center for Macular Degeneration. "There remain many different genes and also many environmental influences to find and study."
"Once we understand the mechanisms sufficiently, we think that it will be possible to intervene perhaps when someone is 40 years old and arrest or slow the disease before it causes damage. We are fortunate that genetics play a major role in AMD because if it had purely environmental causes, we'd probably never figure it out," he added.
Using genetic information to make diagnoses and match treatments to disease is called gene-directed therapy. Because of the variety of causes, no single drug or treatment is likely to work for all people with macular degeneration. However, the fibulin 5 gene finding is one of the genetic clues that clinicians eventually could use to determine the form of macular degeneration for which a patient is at risk and then choose the best prevention.
"As already is done with cancer, clinicians could use genetic tests to identify patients according to the specific mechanism affecting them," Stone said. "In addition, animal models would allow us to develop drugs that are specific to each of these many different forms of macular degeneration."
Finding preventive treatments for macular degeneration is imperative, Stone said. The disease is the leading cause of blindness in Americans age 60 and older, according to the NEI. With the growing number of people living into their 80s and 90s, many countries, including the United States, face an "impending epidemic of blindness," Stone said.
Finding the causes of many eye diseases has taken longer than finding the causes of diseases involving organs such as the skin or liver. With these diseases, a pathologist can often take a piece of tissue from a living person -- a biopsy -- and look for what is wrong. But that approach is not possible with the eye.
"The retina is such a delicate, fragile organ that you can't take a little piece of it from a living patient to find out what's wrong," Stone explained. "For decades, ophthalmologists have been able to look inside the eye and see the drusen but they have not been able to determine biochemically what is wrong with the eye unless patients donate their eyes for research after their death.
"Molecular genetics is a very powerful way for us to understand disease when tissue samples are scarce," Stone added.
In addition to Stone, major contributors to the paper included Terry Braun, Ph.D., assistant professor of biomedical engineering and ophthalmology; Thomas Casavant, Ph.D., UI professor of electrical and computer engineering and biomedical engineering; Stephen Russell, M.D., associate professor of ophthalmology and service director of Vitreoretinal Disease and Surgery; and Val Sheffield, M.D., Ph.D., UI professor of pediatrics and also a Howard Hughes Medical Investigator.
Funding for the study included support from the Carver Endowment for Molecular Ophthalmology and the Foundation Fighting Blindness (www.blindness.org).
Learn more about the UI Center for Macular Degeneration at http://c4md.org/.
University of Iowa Health Care describes the partnership between the UI Roy J. and Lucille A. Carver College of Medicine and UI Hospitals and Clinics and the patient care, medical education and research programs and services they provide. Visit UI Health Care online at http://www.uihealthcare.com.
STORY SOURCE: University of Iowa Health Science Relations, 5137 Westlawn, Iowa City, Iowa 5224-1178
MEDIA CONTACT: Becky Soglin, 319 335-6660 email@example.com
PHOTOS/GRAPHICS: The following images are not copyrighted; however, please credit the National Eye Institute, National Institutes of Health.
Photo simulation of macular degeneration:
Diagrams of the eye, labeled and showing the retina and macula: http://www.nei.nih.gov/photo/eyean/index.asp -- image reference NEA09 or NEA01
Photos of eyes: http://www.nei.nih.gov/photo/eyes/index.asp
VISUAL/AUDIO: A six-minute interview with Dr. Stone and footage of his laboratory are available in various formats, including Beta-SP, DV and VHS. Please specify your format needs in an email to firstname.lastname@example.org or call 319-335-6660.
FOR ADDITIONAL COMMENTARY AND INFORMATION: Contact Allie Laban-Baker, director of public awareness at the Foundation Fighting Blindness in Owings Mills, Md. 410-568-0126 or Alaban-Baker@blindness.org. The foundation's web site is www.blindness.org.
National Eye Institute: http://www.nei.nih.gov/health/