DGM (Dutch-German Mennonite)

Inheritance: X-linked
Genes: NYX

X-linked CSNB
Congenital stationary night blindness
Congenital stationary night blindness with myopia
CSNB1
NBM1

Nyctalopia
Night blindness
Hemeralopia
Myopia

Night Blindness, Stationary, Type 1A

Clinical Characteristics

General description (for patients):

Night blindness, or inability to see well in the dark, has been known for centuries and is a part of several retinal disorders (such as retinitis pigmentosa).  This form seems to be a “pure” disease as it affects the eye only and is usually manifest in males only although transmitted through the female.  Mild to moderate near-sightedness is also almost always present.  This is a non-progressive disorder with a range of severity.  Visual acuity is usually in the range of 20/30 to 20/60.

Medical description:  

This disorder of night blindness is not associated with other retinal disease and is stationary. Many individuals have some degree of myopia but corrected vision remains good and congenital nystagmus is infrequent. The fundus appearance is usually normal.  This condition is sometimes called the complete form but there is evidence of another 'incomplete' form (see type 2A), also X-linked, in which near-sightedness is not a feature.  Rare homozygous females may or may not be symptomatic.  However such females usually have acuities of 20/30 or less as well as an abnormal electroretinograms.  No systemic abnormalities have been reported.

Genetics:

This X-linked form of night blindness is caused by a mutation in the NYX gene located on the X chromosome (Xp11.4).  Thus only males are generally affected but in a Dutch-German Mennonite family in Canada, three homozygous females with mutations on both X chromosomes were identified with characteristic visual and ERG findings.  See Night Blindness, Stationary type 2A for a more complete description of the genetic and phenotypic features of the several varieties of CSNB.

Treatment:

Beyond correction for myopia, no treatment is available.

Prognosis:

Excellent with correction of refractive error.

Ancillary treatments and support:

Vision training, vocational rehabilitation.

Specialists and specialty centers:

Ophthalmologist, low vision specialist.

References:

Bech-Hansen, N.T., and Pearce, W.G.:  Manifestations of X-linked congenital stationary night blindness in three daughters of an affected male:  demonstration of homozygosity.  Am. J. Hum. Genet. 52: 71-77, 1993.  PubMed ID: 8434607

Pusch, C.M., Zeitz, C., Brandau, O., Pesch, K., Achatz, H., Feil, S., Scharfge, C., Maurer, J., Jacobi, F.K., Pinckers, A., Andreasson, S., Hardcastle, A., Wissinger, B., Berger, W., and Meindl, A.:  The complete form of X-linked congenital stationary night blindness is caused by mutations in a gene encoding a leucine-rich repeat protein.  Nature Genet. 26: 324-327, 2000.  PubMed ID: 11062472