"If you have abnormalities or decreased functioning of the drainage structures, the input of aqueous humor can result in increased intraocular pressure and the very nasty glaucoma that human infants suffer," he said. "This can be a painful condition with pressures high enough to tear the cornea and risk loss of vision."
One puzzle confronting researchers, said John, is that some infants with the inherited condition can suffer serious glaucoma, while others either show delayed effects or none at all. "So, although it is not widely accepted, we believed that there could be multiple genetic and/or environmental factors that could affect the course of the disease," he said. Such factors could interact with one another to compromise the intricate drainage structures to a greater degree in some cases than in others, said John.
A clue to one possible genetic factor arose from observations that albino mice lacking Cyp1b1 appeared to show worse pathology than pigmented mice. A series of genetic crosses of various mice by Libby and his colleagues produced strains of mice whose only difference was the presence or absence of pigmentation. The researchers ultimately pinpointed the key modifier of severity of glaucoma, showing that in the Cyp1b1-negative mice it hinged on the status of the gene that encodes the enzyme tyrosinase. The tyrosinase enzyme is involved in the pigmentation process as a key catalyst for converting the amino acid tyrosine to a precursor pigment molecule, L-DOPA.
The researchers also explored how mutations in the gene for tyrosinase affected mice lacking the FOXC1gene, which also causes PCG and other forms of glaucoma in humans. They found that the tyrosinase-deficient, FOXC1-mice also showed more severe abnormalities in their ocular drainage system.
To determine whether administering L-DOPA might alleviate the
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Contact: Joyce Peterson
joyce@jax.org
207-288-6058
Jackson Laboratory
7-Mar-2003