Clinical Guidance

No genotype-phenotype correlations are known.

Source: GeneReviews — "X-Linked Congenital Stationary Night Blindness"

Penetrance

Penetrance of X-linked CSNB is probably 100%, but expressivity is variable ; individuals with mild presentations may be missed if electroretinography is not performed.

Source: GeneReviews — "X-Linked Congenital Stationary Night Blindness"

Diagnostic Criteria

Suggestive Findings Males. X-linked congenital stationary night blindness (CSNB) should be suspected in a male proband with the following characteristic clinical and electroretinogram (ERG) findings characteristicec of complete X-linked CSNB or incomplete X-linked CSNB : Characteristic clinical findings: • Reduced visual acuity • Night blindness • Myopia • Nystagmus (not universal) and strabismus (50%-70%) • Normal color vision • Normal fundus examination • Family history consistent with X-linked inheritance Characteristic findings on ERG examination: • ERG is used to assess the changes in electrical activity of the retina in response to light. The b-wave is caused by the depolarization of ON bipolar cells in response to light stimuli and is strictly dependent on synaptic transmission from photoreceptors to ON bipolar cells. • Individuals with X-linked CSNB have reduced scotopic b-wave amplitudes in response to bright flashes after dark adaptation. The resulting ERG waveform is essentially a negative wave (amplitude of the a-wave is larger than the b-wave, not reaching the baseline) , referred to as the Schubert-Bornschein form . • The ERG can define specific retinal dysfunctions and, in general, differentiate the forms of X-linked CSNB, thereby identifying the gene most likely to be involved . Table 1. Electroretinogram Findings in Complete and Incomplete X-Linked Congenital Stationary Night Blindness

Source: GeneReviews — "X-Linked Congenital Stationary Night Blindness"

Differential Diagnosis

Only a few conditions may initially be confused with the X-linked form of congenital stationary night blindness (CSNB). Table 4. Disorders to Consider in the Differential Diagnosis of X-Linked Congenital Stationary Night Blindness

Management Guidelines

Evaluations Following Initial Diagnosis

To establish the extent of disease in an individual diagnosed with X-linked congenital stationary night blindness (CSNB), the following evaluations (if not performed as part of the evaluation that led to the diagnosis) are recommended:

• Ophthalmologic examination

• Electroretinography

• Dark adaptation (optional)

• Consultation with a clinical geneticist and/or genetic counselor

Treatment of Manifestations

Coincident high myopia or hyperopia can be managed with glasses or contact lenses. Occasionally, a boy with X-linked CSNB may adopt a cosmetically unacceptable or functionally awkward head posture to dampen the degree of nystagmus in a particular position of gaze (the so-called "null point"). In some instances the position of gaze for the null point may be shifted to a better functional range by carefully planned strabismus surgery.

Surveillance

Regular (yearly) eye examinations are recommended with refraction at a young age to monitor for the development of myopia.

Agents/Circumstances to Avoid

Reduced visual acuity and difficulties seeing at night may preclude driving a car or restrict the class of driving license.

Evaluation of Relatives at Risk

For infants identified with high myopia, unusual head posture, or nystagmus and a family history of CSNB, ophthalmic examination and molecular genetic testing may confirm the diagnosis of CSNB, obviating the need for neuroimaging or clinical electrophysiologic testing under sedation or general anesthesia.

Source: GeneReviews — "X-Linked Congenital Stationary Night Blindness"

Clinical Guidance

Reduced visual acuity and difficulties seeing at night may preclude driving a car or restrict the class of driving license.

Source: GeneReviews — "X-Linked Congenital Stationary Night Blindness"

Therapies Under Investigation

Search ClinicalTrials.gov in the US and EU Clinical Trials Register in Europe for information on clinical studies for a wide range of diseases and conditions. Note: There may not be clinical trials for this disorder.

Source: GeneReviews — "X-Linked Congenital Stationary Night Blindness"

Surveillance Guidelines

Regular (yearly) eye examinations are recommended with refraction at a young age to monitor for the development of myopia.

Source: GeneReviews — "X-Linked Congenital Stationary Night Blindness"