Researchers from Johns Hopkins had discovered the gene expression responsible for extreme farsightedness in people.
The researchers report that nanophthalmos, or "dwarf eye," a rare, potentially blinding disorder, is caused by an alteration in a gene called MFRP that helps control eye growth and regulates the organ's shape and focus. The study is described in the July issue of the journal Proceedings of the National Academy of Sciences.
As the child grows and gains more visual experience, the eye adjusts its focus by growing, which changes the distance between the lens and the retina, the light-detecting layer of cells at the back of the eye. Due to natural genetic mutations, some eyes stop growing too soon, causing farsightedness.
In the case of nanophthalmos, a mutation in MFRP completely wipes out the function of the protein coded for by the gene. In people with this condition, the retina is too close to the lens, but the lens and cornea, the eye's outermost layer, are of normal size and shape.
Eyes with nanophthalmos still work quite well, despite these complications. But the disease's secondary complications later in life, including glaucoma or detached retina, are far more severe and can lead to complete blindness.
One such patient with nanophthalmos, an Amish-Mennonite woman who was blind in one eye, came to the Wilmer Eye Institute in 1998 for treatment. By reconstructing the woman's family tree, the researchers discovered that several living relatives also suffered from nanophthalmos, and four deceased relatives had been part of the classic Johns Hopkins Bloomberg School of Public Health study in the 1970s that helped define the disease as genetic.
In the study, the researchers examined the woman's DNA for possible gene mutations causing nanophthalmos. The research team successfully mapped the MFRP gene mutation in humans and discovered that the protein was completely missing from nanophthalmos patients. In a normal human eye, the MFRP protein is located on the surface of the retinal pigment epithelium (RPE), which is located beneath the retina and helps maintain photoreceptors, the eye's light-detecting cells. Blindness occurs when these cells die after detachment of the retina from the RPE.
Researchers hope the information gained from his study will open doors to correcting other types of severe refractive error, not only farsightedness, but also nearsightedness.