June 3, 2008 Research by Gu Zhu, M.D., and colleagues supports the theory that the refractive errors known as nearsightedness and farsightedness are primarily inherited. The group also identified the probable location---on the long arm of chromosome 5---of genes that help determine axial length, a key factor in these refractive errors. Axial length is a specific measurement from the front to back of the eye; this distance is longer than normal when a person is nearsighted and shorter than normal in a farsighted person.
Dr. Zhu's study focused on nearsightedness, or myopia, building on previous research on genetic aspects and environmental factors. Myopia compromises the eye's ability to focus on and see objects clearly at a distance. Especially when myopia is severe, it is expensive to treat and costly to patients' quality of life. The disorder is on the rise in the United States and globally and research efforts have intensified accordingly.
Dr. Zhu's team recruited 893 individuals from the Tasmania Twin Eye Study and Brisbane Adolescent Twin Study (BATS), Australia, and obtained axial length measurements. They analyzed the proportional impacts of genetic and environmental factors on axial length in this sample of identical and fraternal twins, and found that genetic factors explained approximately 80 percent of the axial length values, after adjusting for age and sex. This study breaks new ground in linking axial length to the heritability of refractive error. Research team member David Mackey, M.D., said that new measurement techniques will likely make collection of axial length data routine in future research on myopia and other refractive error.
By performing a genome scan on a subset of 318 individuals, the researchers found "strong evidence" for the role of chromosome 5 (specifically the 5q region) in the inheritance of axial length. Dr. Zhu's team has launched a genomic analysis of a larger study group to confirm and refine this finding. Other studies have suggested that environmental factors such as regular periods of outdoor play during childhood---rather than having children concentrate only on reading and other "near work"---might help reduce the development of nearsightedness, at least in those who are genetically susceptible. Identifying strong genetic markers could further this and other preventive efforts.
This research was published in the June 2008 issue of Ophthalmology.
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