The Genetic Basis for Normal Vision and Vision Disorders

Abstract

The genes encoding the long‐(L) and middle‐(M) wavelength sensitive cone photopigment opsins are located on the X‐chromosome, and the gene encoding the short‐(S) wavelength sensitive opsin is on chromosome 7. Inherited red‐green color vision deficiencies are quite common and are most often associated with deletions or rearrangements of the L and M cone opsin genes. The same genetic mechanism that produces the gene deletions and rearrangements of the L and M opsin genes also intermixes their sequences producing new opsins that are chimeras of the ancestral L and M opsins. Inherited colorblindness is usually presumed to be strictly congenital. Some of the chimeric opsins produce nonfunctional photopigments; however, others cause a progressive loss of cone function, and thus are associated with red‐green color vision deficiency that is inherited but not congenital. Inherited blue‐yellow color vision deficiencies are much rarer, and are associated with mutations of the S opsin gene. Mutations in the S opsin can cause an S cone dystrophy and color vision defects that are also inherited but not congenital.