CSNB

Night blindness is a feature of many pigmentary and other retinal disorders, most of which are progressive.  However, there is also a group of genetically heterogeneous disorders, with generally stable scotopic defects and without RPE changes, known as congenital stationary night blindness (CSNB).  At least 10 mutant genes are responsible with phenotypes so similar that genotyping is usually necessary to distinguish them.  All are caused by defects in visual signal transduction within rod photoreceptors or in defective photoreceptor-to-bipolar cell signaling with common ERG findings of reduced or absent b-waves and generally normal a-waves.  However, the photopic ERG can be abnormal to some degree as well and visual acuity may be subnormal.  In the pregenomic era, subtleties of ERG responses were frequently used in an attempt to distinguish different forms of CSNB.  Genotyping now enables classification with unprecedented precision.

Congenital stationary night blindness disorders are primarily rod dystrophies presenting early with symptoms of nightblindness and relative sparing of central vision.  Nystagmus and photophobia are usually not features.  Dyschromatopsia and loss of central acuity can develop later as the cones eventually become dysfunctional as well but these symptoms are much less severe than those seen in cone-rod dystrophies.  The amount of pigmentary retinopathy is highly variable.

This disorder (CSNBAD3), one of three autosomal dominant CSNB conditions, is known primarily from  a single large family in Southern France.  All affected individuals descended from Jean Nougaret from which the eponym is derived.  The published pedigree by F. Cunier in 1838 is probably the first illustrating autosomal dominant inheritance of a human disease.  Rod a-waves are completely absent suggesting complete lack of rod function.  Night vision in dim conditions was reduced but not with bright backgrounds.  Daytime vision is normal as is color vision.  Rare patients have peripheral pigmentary changes with visual field restriction.

Night blindness is a feature of many pigmentary and other retinal disorders, most of which are progressive.  However, there is also a group of genetically heterogeneous disorders, with generally stable scotopic defects and without RPE changes, known as congenital stationary night blindness (CSNB).  At least 10 mutant genes are responsible with phenotypes so similar that genotyping is usually necessary to distinguish them.  All are caused by defects in visual signal transduction within rod photoreceptors or in defective photoreceptor-to-bipolar cell signaling with common ERG findings of reduced or absent b-waves and generally normal a-waves.  However, the photopic ERG can be abnormal to some degree as well and visual acuity may be subnormal.  In the pregenomic era, subtleties of ERG responses were frequently used in an attempt to distinguish different forms of CSNB.  Genotyping now enables classification with unprecedented precision.

Congenital stationary night blindness disorders are primarily rod dystrophies presenting early with symptoms of nightblindness and relative sparing of central vision.  Nystagmus and photophobia are usually not features.  Dyschromatopsia and loss of central acuity can develop later as the cones eventually become dysfunctional as well but these symptoms are much less severe than those seen in cone-rod dystrophies.  The amount of pigmentary retinopathy is highly variable.

This disorder (CSNBAD2) is one of three autosomal dominant CSNB conditions.  ERG responses were identical to those found in the Nougaret type of autosomal dominant CSNB.  Rod a-wave responses to single flashes are completely absent suggesting complete lack of rod function.  The residual b-wave suggests some cone response.  Daytime and color vision are normal.

Night blindness is a feature of many pigmentary and other retinal disorders, most of which are progressive.  However, there is also a group of genetically heterogeneous disorders, with generally stable scotopic defects and without RPE changes, known as congenital stationary night blindness (CSNB).  At least 10 mutant genes are responsible with phenotypes so similar that genotyping is usually necessary to distinguish them.  All are caused by defects in visual signal transduction within rod photoreceptors or in defective photoreceptor-to-bipolar cell signaling with common ERG findings of reduced or absent b-waves and generally normal a-waves.  The photopic ERG is usually abnormal to some degree as well and visual acuity may be subnormal.  In the pregenomic era, subtleties of ERG responses were frequently used in an attempt to distinguish different forms of CSNB.  Genotyping now enables classification with unprecedented precision.

Congenital stationary night blindness disorders are primarily rod dystrophies presenting early with symptoms of nightblindness and relative sparing of central vision.  Nystagmus and photophobia are usually not features.  Dyschromatopsia and loss of central acuity can develop later as the cones eventually become dysfunctional as well but these symptoms are much less severe than those seen in cone-rod dystrophies.  The amount of pigmentary retinopathy is highly variable. 

In this disorder (CSNB1C) the b-wave responses are severely deficient (no scotopic response) and a-waves seem to be normal.  Some reduction in central acuity is common.  High myopia may be present together with nystagmus and strabismus.  In one family, hypoplastic discs and relative thinning of the inner nuclear layer were described in twin brothers.  ERG responses suggest loss of ON bipolar cell function similar to that found in patients with GRM6 mutations (CSNB1B; 257270).

Night blindness is a feature of many pigmentary and other retinal disorders, most of which are progressive.  However, there is also a group of genetically heterogeneous disorders, with generally stable scotopic defects, known as congenital stationary night blindness (CSNB).  At least 10 mutant genes are responsible with phenotypes so similar that genotyping is usually necessary to distinguish them.  All are caused by defects in visual signal transduction within rod photoreceptors or in defective photoreceptor-to-bipolar cell signaling with common ERG findings of reduced or absent b-waves and generally normal a-waves.  However, the photopic ERG can be abnormal to some degree as well and visual acuity may be subnormal.  In the pregenomic era, subtleties of ERG responses were frequently used in an attempt to distinguish different forms of CSNB.  Genotyping now enables classification with unprecedented precision.

Congenital stationary night blindness disorders are primarily rod dystrophies presenting early with symptoms of nightblindness and relative sparing of central vision.  Nystagmus and photophobia are usually not features.  Dyschromatopsia and loss of central acuity can develop later as the cones eventually become dysfunctional as well but these symptoms are much less severe than those seen in cone-rod dystrophies.  The amount of pigmentary retinopathy is highly variable.

In this disorder (CSNB1B) the b-wave responses are severely deficient and a-waves seem to be normal.  Color vision is normal and refractive errors are unremarkable.  Visual acuity ranges from normal to a mild reduction (20/15-20/40).  One patient with 20/40 vision has been reported to have bone spicule pigment clumps in the midperiphery. Several patients with subnormal vision have been reported to have nystagmus.

Patients have a distinctive ERG pattern response to scotopic 15-Hz flicker stimuli that suggest that more than two rod neural pathways exist.