Age related macular degeneration is the most common cause of legal blindness in developed countries. It affects about six percent of Americans between the ages of 65 and 75, and almost 20% of those over 75. In this condition, yellowish deposits called drusen accumulate beneath a part of the eye known as the retina and cause it to lose some of its function. Because the central part of the retina, known as the macula, is most affected, this process is called "macular" degeneration.
It has been known for nearly 100 years that there are some forms of macular degeneration that are inherited. In fact, Best's disease, which can affect children as young as one year of age, has been referred to as "juvenile macular degeneration". Other conditions known as "dominant drusen," "cuticular drusen," and "pattern dystrophy," are also inherited and can cause visual problems very similar to age related macular degeneration.
Because inherited conditions can be studied with powerful molecular techniques more easily than non-inherited ones, we have been applying such methods to the study of inherited forms of macular degeneration in the hope that a better understanding of these conditions will lead to better treatment for the more common age-related disorder. We have been using a technique known as chromosome linkage analysis to look for genes that cause macular degeneration. Families with inherited macular degeneration are examined and blood samples are taken for DNA analysis. Then, a computer program looks for a relationship between certain "markers" in the DNA and the presence of the macular disease.
Dr. Sheffield draws blood during a recent field trip.
Since we began this study in 1987, over 2000 patients have agreed to participate and have been examined. To date, we have mapped the gene locations for three macular dystrophies and have identified mutations in a gene responsible for another. This findings are described below.
Best's disease
Stargardt-like dominant progressive macular dystrophy
Autosomal dominant radial drusen (Malattia leventinese)
Pattern dystrophy
