Age-related macular degeneration (AMD) is the leading cause of blindness in individuals over 55 years of age in the developed world. AMD affects about 11 million Americans, 5 million of whom have become legally blind because of it. Stargardt's macular degeneration (STGD3) is an early-onset form of AMD that affects about 30,000 children and young adults in the United States. Researchers reported in this week's
The gene, designated ELOVL4, was found to be the cause of Stargardt's macular degeneration and another form of macular degeneration called autosomal dominant macular atrophy (adMO). In both conditions, debris called lipofuscin accumulates in the retinal pigment epithelium (RPE) and results in its degeneration together with photoreceptor cells, followed by a loss of vision.
Genetic mapping data suggested that mutations in a single gene might be responsible for both conditions, already known to bear clinical resemblance. A twenty-member research team from Johns Hopkins University, the Cleveland Clinic, University of Colorado at Boulder, University of Michigan, the University of Alberta and Merck & Company found the gene ELOVL4 was present in all affected members of STGD3 and adMO families. Bioinformatic analysis of ELOVL4 revealed that it is homologous with a group of yeast proteins that function in the biosynthesis of very long chain fatty acids.
"This important finding uncovers a new pathway in macular degeneration and will allow us to create an animal model to test potential drug therapies for both Stargardt's macular degeneration and age-related macular degeneration," said team member Kang Zhang of the Cole Eye Institute of the Cleveland Clinic.
"The most immediate benefit from isolating the gene responsible for two dominant forms of macular dystrophy is clarification of the pathogenic mechanisms involved in macular degeneration," Dr. Zhang added. "Although disease genes responsible for four other forms of inherited macular dystrophies have been identified, our results are the first to implicate the biosynthesis of long chain fatty acids in the pathogenesis of at least two related forms of macular degeneration."
Dr. Zhang believes future drugs could one day let doctors regulate the eye's production of fatty acids, slowing the build-up of harmful debris. At the Cleveland Clinic, Zhang directs a genetics laboratory where potential drug treatments for macular degeneration will be tested on mice implanted with the newly isolated gene.
While the isolation of the ELOVL4 gene and determination of its structure are certainly an accomplishment, the real achievement is being able to use this discovery to identify a possible mode of drug action to combat the blindness the gene causes.