Molecular Genetics of Juvenile Onset Glaucoma

Glaucoma is a major human eye disease which has blinded about 80,000 out of the 2,000,000 Americans which are affected by it. Even though some forms of treatment have been developed, including both medications and surgery, a precise understanding of this disease on the cellular and biochemical level is lacking. Recent medical research advances are allowing scientists to use molecular biology and a technique called reverse genetics to gain understanding of some human disease processes. The reverse genetics approach involves finding out where a gene is located on one of the human chromosomes and using that information to lead to the cloning of the gene responsible for the disorder. The critical element for this research approach is a very large family in which glaucoma is inherited and present in several living generations of the family at once. Such families are rare and the family which we have identified for this study is a very valuable one. The purpose of this project is to continue a molecular genetic study of a form of juvenile glaucoma which is inherited in a large multigenerational family in Michigan which we have been studying. This family is very valuable to our study for several reasons, including the size of the family and the early age of onset. We have spent this year collecting blood samples and carrying out clinical examinations on members of this family. We have made DNA from blood and made cell lines which can be frozen away so that more DNA can be made in the future. We have examined each family member to determine whether they have glaucoma, whether they have elevated pressure inside their eyes, whether they have had surgery to help control the pressure, and whether they have suffered nerve damage and vision loss. We have found that the form of glaucoma in this family begins young, and most of the standard drug therapies do not work well enough to reduce the pressure inside of the eye. In most cases the glaucoma patients have had surgery several times by their late teens. Several members of the family have gone blind and there is no doubt that this form of glaucoma is severe. This grant will allow us to carry out the next steps in a reverse genetics approach to this family: a genetic linkage analysis aimed at finding a DNA probe located near the glaucoma gene which is defective in affected members of this family. This will allow us to tell where this glaucoma gene is located on one of the human chromosomes. Finding the location of the gene will take may very well take years, but it is the first and critical step towards obtaining a cloned glaucoma gene. The long range goal of our research group is to find the gene responsible for causing a type of glaucoma which is very hard to treat with some of the usual kinds of drugs. A cloned glaucoma gene would aid in studies of the underlying biochemical causes of glaucoma and lead to improved methods for treating, and perhaps eventually curing, one form of glaucoma. Such a clone would allow us to study the function of the gene, to develop new assays for potentially therapeutic drugs, and to give much more precise information to patients about what is causing their disease. Such a clone would help us develop tests to distinguish between different kinds of glaucoma so that the optimal therapy might be assigned based on precise understanding of the defect. The advances that will come from cloning a glaucoma gene are sorely needed. In spite of a variety of drug therapies and surgical approaches to glaucoma blindness cannot always be prevented. Many who are not completely blind have reduced vision, and everyone who suffers from glaucoma faces a lifetime of pressure monitoring, visual testing, drug therapies, possibly multiple surgeries, and fear of eventual blindness. The juvenile-onset form of glaucoma which we propose to study is especially frightening because it begins so early in life and there is so little prospect of success with drug therapies. The approach we will use, called positional cloning, has been used recently with dramatic success to clone genes responsible for diseases such as Cystic Fibrosis. By this approach, researchers use the genetic location of a gene as· the mechanism for locating and then cloning a gene which cannot be cloned by the standard methods which require that we know something about the biochemistry, structure and function of the gene product. In the case of Cystic Fibrosis, they first mapped the gene, then used that information to carry out some very sophisticated molecular cloning techniques. The clone they obtained has lead researchers to functional insights about the gene, has allowed them to do genetic screening, and has even lead to an experiment in which a “good” copy of the Cystic Fibrosis gene was used to restore proper functioning to cells with the Cystic Fibrosis defect which were being grown in culture. Many of us are watching with great excitement to see what possibilities for gene therapy will come out of the current studies on the Cystic Fibrosis gene. Similar thinking about glaucoma must await both advances in gene therapy technology and the cloning of a glaucoma gene. With the money from this grant we will examine the genetic material DNA which we have obtained from this family so that we can eventually find out what chromosome the gene is on and where on that chromosome the gene is located. We will hire technical assistance and buy supplies needed to carry out genetic tests on DNA from every member of the family. Once the gene has been mapped we will then have the information we need to proceed towards the cloning of this glaucoma gene.