Inheritance: autosomal dominant
autosomal recessive
X-linked
Genes: CACNA1F
CSNBX

DGM (Dutch-German Mennonite)

CSNB2
CSNB incomplete

Night blindness
Decreased visual acuity
Incomplete CSNB
Nystagmus
Refractive error

Night Blindness, Stationary, Type 2A

Clinical Characteristics

General description (for patients):

Non-progressive night blindness beginning at birth is the outstanding visual symptom of this retinal disease.  Vision is usually mildly to moderately reduced.  The retina appears normal which helps distinguish this condition from others that show pigmentary changes.  Near sightedness can be present in some patients, a feature which is more prominent in a similar condition (type 1A), also transmitted by females and generally found only in males.  “Dancing eyes”, or nystagmus, is noted in some but not all patients.

Medical description: 

Stationary night blindness in the absence of retinal pigmentary changes is characteristic of several disorders (see also type 1A).  A negative electoretinogram is diagnostic (depressed b wave), and no systemic abnormalities are associated.  Nystagmus may be present.  In type 2A, myopia is not as significant a feature (hence the designation as the incomplete form of CSNB) but some decrease in visual acuity is common.  It has been suggested that subtle differences in the ERG of the two disorders may be of more value in distinguishing between the complete and incomplete forms.  Genomics provide the definitive diagnosis.

Genetics:

The genetics of the congenital, stationary night blindness disorders remain to be conclusively delineated.  There are autosomal dominant and recessive forms, and most likely at least three X-linked ones.  The one described here has been found in 17 ‘apparent’ Mennonite families in Western Canada in which the mutation was localized to Xp11.23 presumably involving the calcium channel gene CACNA1F.  Subsequent analysis of this gene in seven Japanese patients with the incomplete form identified five novel mutations.  Another condition, CSNBX, with similar clinical findings is located at Xp21.1.

Treatment: 

No treatment beyond correction of the refractive error is available.

Prognosis: 

This is a stationary disorder and, provided acuity is better than 20/50, patients can live a normal life.

Ancillary treatments and support:

Visual training and aids as necessary.

Specialists and specialty centers:

Ophthalmologist, low vision specialist.

References:

Boycott, K.M., Pearce, W.G., Musarella, M.A., Weleber, R.G., Maybaum, T.A., Birch, D. G., Miyake, Y., Young, R.S., and Bech-Hensen, N.T.:  Evidence for genetic heterogeneity in X-linked congenital stationary night blindness.  Am. J. Hum. Genet. 62: 865-875. 1998.  PubMed ID: 9529339

Nakamura, M., Ito, S., Terasaki, H., and Miyake, Y.:  Novel CACNA1F mutations in Japanese patients with incomplete congenital stationary night blindness.  Invest. Ophthal. Vis. Sci. 42: 610-616, 2001.  PubMed ID: 11381068

Bech-Hensen, N.T., Naylor, M.J., Maybaum, T.A., Pearce, W.G., Koop, B., Fishman, G.A., Mets, M., Musarella, M.A., and Boycott, K.M.:  Loss-of-function mutations in a calcium-channel alpha 1-subunit gene in Xp11.23 cause incomplete X-linked congenital stationary night blindness.  Nature Genet. 19: 264-267, 1998.  PubMed ID: 9662400

Bergen, A.A.B., ten Brink, J.B., Riemslag, F., Shuurman, E.J.M., Merire, F., Tijmes, N., and de Jong, P.R.V.M.  Conclusive evidence for a distinct congenital stationary night blindness locus in Xp21.1.  J. Med. Genet. 33 869-872, 1996.  PubMed ID: 8933343