OMIM ID:
Oguchi Disease, Type 2
Alternate Names
Defective Genes
Clinical Characteristics
Ocular Features
The distinctive feature of Oguchi disease is the peculiar and distinctive discoloration of the fundus under various light conditions, known as the Mizuo phenomenon. Typically, the fundus assumes a golden or gray-white coloration under light adapted conditions but this disappears during acute dark adaptation and only reappears after prolonged time spent in darkness. Rod dark adaptation is markedly delayed while that of cones is normal. Single flash cone and 30Hz flicker responses are markedly reduced. Visual acuity, visual fields and color vision are all normal. A- and b-waves on single flash ERG are decreased or absent under lighted conditions but increase after prolonged dark adaptation. Night blindness is present from birth without progression.
Systemic Features
No systemic abnormalities are associated with Oguchi disease.
Genetics
Inheritance
Oguchi type 2 disease is an autosomal recessive condition caused by mutations in the rhodopsin kinase (GRK1) gene (13q34) whose product works with arrestin in turning off rhodopsin after light activation as part of the dark adaptation mechanism.
Oguchi type 1 disease (258100) is a similar form of congenital stationary nightblindness caused by mutations in the SAG gene.
Pedigree
Autosomal recessive
In order for autosomal recessive disorders to be expressed, offspring generally must inherit two mutations, one from each carrier parent. Carriers with only one mutation, such as the parents, do not have clinical disease. Note that carrier parents can expect that 1 in 4 children (25%) will inherit both mutations and have the disorder, 2 in 4 children (50%) will be carriers like their parents, while 1 in 4 children (25%) inherit neither mutation.
In order for autosomal recessive disorders to be expressed, offspring generally must inherit two mutations, one from each carrier parent. Carriers with only one mutation, such as the parents, do not have clinical disease. Note that carrier parents can expect that 1 in 4 children (25%) will inherit both mutations and have the disorder, 2 in 4 children (50%) will be carriers like their parents, while 1 in 4 children (25%) inherit neither mutation.