GLAUCOMA
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Heredity and Glaucoma

Glaucoma Often Occurs in Families

If you have glaucoma, there is a good chance that someone else in your family may have it, too. For primary open-angle glaucoma, the most common form of glaucoma, there is approximately a one-in-five chance that a close relative also has glaucoma. For some less common forms of glaucoma, such as Rieger’s syndrome and glaucoma of childhood, the risk of brothers or sisters and children developing the disease is close to 50%.

The heritable nature of glaucoma means that your brothers, sisters, and children need to obtain regular eye examinations, especially after age 40. If your glaucoma was first detected at a young age, then your relatives should be examined at an earlier age, too. They should be told to let their eye doctor know that they have a close relative with glaucoma so that careful attention can be directed at examination of the optic nerve.

Good News About Glaucoma
The good news about the heritable nature of glaucoma is that it permits the use of powerful new scientific tools of molecular genetics to study glaucoma. Molecular genetic studies have made great strides in recent years in providing important information about other inherited diseases such as cystic fibrosis, Huntington’s disease, and retinitis pigmentosa. There is a good reason to believe that they will provide important new information about glaucoma, as well.

Since 1987, molecular genetic studies have been directed at discovering new information about glaucoma. Progress has been made in finding the region of DNA that is defective for some forms of glaucoma, including Rieger’s syndrome, juvenile open-angle glaucoma, iris hypoplasia, and aniridia. Even though these are uncommon forms of glaucoma, they have features that make them easier to study than primary open-angle glaucoma. Both Rieger’s syndrome and aniridia are sometimes seen as part of a group of abnormalities caused by rearrangements in a patient’s chromosomes. These rearrangements can be seen under the microscope, and serve as road maps leading scientists to the exact spot where the defective gene lies. In the cases of juvenile open-angle glaucoma and iris hypoplasia, the young age at which glaucoma develops and the 50% risk of being affected leads to families in which many members have glaucoma. This enables the genetic make-up of these affected individuals to be determined.

Even though primary open-angle glaucoma is by far the most common form of glaucoma in the United States, it is difficult to study its genetic basis. Unlike the juvenile forms of glaucoma, primary open-angle glaucoma strikes fairly late in life, when the affected individual’s parents and some brothers and sisters may no longer be living. The next generation may not yet be old enough to show early evidence of the disease. Because of this, single families large enough to study have not been identified. Therefore, many smaller families will need to be pooled to find the affected region.

Possible Benefits of Genetics Research in Glaucoma
How will this type of research help patients with glaucoma? If scientists can find the defective gene or genes that cause glaucoma, we should be able to identify the precise substances responsible for causing it. This knowledge will allow us to better understand the mechanisms that cause glaucoma.

This understanding might dramatically change the way we treat glaucoma. In the distant future, it may be possible to replace a glaucoma-causing gene and either prevent glaucoma or more effectively treat it. A more immediate benefit would be the development of treatment directed at replacing or altering substances made by the defective genes. We might even envision a day when a patient would take a specific medication to treat the underlying cause of his or her glaucoma, rather than just lowering eye pressure.

It may also be possible to develop blood tests that can be used to screen for individuals at risk for glaucoma long before eye pressure is increased, before the optic nerve is damaged, and before the loss of visual field. In some families that have many members with childhood glaucoma, we can already determine by a blood test which children will develop glaucoma and which children will not. The hope is that this type of testing may someday be available for all forms of glaucoma.