Monday, February 12, 2007

Section 11-C(1): Juvenile open angle glaucoma

Juvenile open angle glaucoma (JOAG) is a rare form of glaucoma that accounts for approximately 1% of total cases. The clinical features of JOAG are the same as those of more common forms of glaucoma (such as POAG). JOAG differs from POAG mainly in the severity of disease and age of onset. Patients with JOAG develop disease at a much earlier age than patients with POAG (between 3 and 40 years of age). JOAG patients also have very high intraocular pressures that frequently exceed 40 mm Hg in the absence of treatment.

In many cases, JOAG clearly runs in families as a dominant trait. Due to the early age of onset and the strong clinical signs of JOAG, several large pedigrees with many generations of affected family members have been recognized (Figure 11-2).

Figure 11-2

Figure 11-2. Juvenile open angle glaucoma (JOAG) pedigree. JOAG is an early-onset form of open angle glaucoma that is inherited as an autosomal dominant trait. Offspring of a parent with JOAG have up to a 50% chance of inheriting JOAG. This diagram shows the pattern of inheritance of glaucoma through an actual JOAG pedigree.

Genetic studies of large families (like the one shown in Figure 11.2) demonstrated that defects or mutations in the myocilin gene are a cause of JOAG. Most cases of JOAG that have a strong family history of disease are associated with defects in the myocilin gene (MYOC). Myocilin associated glaucoma is inherited as an autosomal dominant trait. That is, patients carrying a myocilin mutation that causes JOAG have a 50% chance of passing the gene (and high risk for glaucoma) to their children. Several specific defects or mutations in the myocilin gene that cause JOAG have been identified.

Some patients have the typical clinical features of JOAG but do not have a family history of disease. The myocilin gene has a less important role in these sporadic cases of JOAG.

The myocilin gene directs tissues of the eye to produce a protein that is released into the aqueous humor. The myocilin protein has an unknown function; however, glaucoma develops when its structure is altered by a mutation. Studies are underway to investigate role of the myocilin gene in healthy eyes and the process by which defects in this gene lead to glaucoma.

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