OMIM ID:
Night Blindness, Congenital Stationary, CSNB1E
Alternate Names
Defective Genes
Clinical Characteristics
Ocular Features
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 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.
The onset of night blindness in type 1E occurs in early childhood and may be congenital. Some degree of nystagmus is usually present. It is usually only slowly progressive.
Systemic Features
No systemic disease is associated with congenital stationary night blindness.
Genetics
Inheritance
This type of congenital stationary night blindness is inherited in an autosomal recessive pattern resulting from homozygous or compound heterozygous mutations in GPR179. The gene encodes an orphan G protein receptor.
Other autosomal recessive CSNB disorders are: CSNB2B (610427), CSNB1B (257270), and CSNB1C (613216).
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.