A decade in search of myopia genes.

Nearly half of visual impairment in the world is caused by uncorrected refractive errors, and myopia constitutes a significant proportion of this problem. Moreover, the prevalence of myopia is increasing, especially in Asian countries. Linkage studies have identified at least 18 possible loci (MYP) in 15 different chromosomes associated with myopia, although some of these remain to be confirmed. However, when studies have been carried out to identify specific candidate genes, it is apparent that these genes are often not part of MYP loci. In studying the expression of specific genes that might be responsible for myopia, we are learning that the involvement of various small leucine-rich repeat proteoglycans and growth factors is not a simple one. The emerging picture is one of complex interaction, in which mutations in several genes likely act in concert. The majority of myopia cases are not likely caused by defects in structural proteins, but in defects involving the control of structural proteins. The future of genetic research in this area will likely rely increasingly on microchip array technology.