Congenital Stationary Night Blindness, X-Linked

Congenital stationary night blindness (CSNB) is a group of congenital retinal dystrophies currently associated with two X-linked genes (NYX, CACNA1F), six autosomal recessive genes (CABP4, GRK1, GRM6, RDH5, SAG, TRPM1), and three autosomal dominant genes (GNAT1, PDE6B, RHO). CSNB can be subcategorized into two subgroups, “complete” or “incomplete,” defined by the presence or the absence of residual rod function measured by dark adaptometry or electroretinogram (ERG). The NYX and the TRPM1 gene mutations are mainly responsible for the complete form of CSNB. Patients with complete X-linked CSNB usually have high myopia with a tigroid-appearing fundus. Some patients have mild nystagmus. All patients with stationary night blindness have an abnormal dark-adaptation curve and an abnormal ERG. The ERG demonstrates a severely reduced or absent dark-adapted rod-mediated b-wave response (Pusch et al., 2000 and Bech-Hansen et al., 2000). In particular, this analysis will produce a subnormal ratio of b-wave to a-wave amplitude when using a white flash in the dark (Pusch et al., 2000 and Bech-Hansen et al., 2000). Reduced oscillatory potentials and cone ERGs that are normal to mildly abnormal are also typical findings (Pusch et al., 2000 and Bech- Hansen et al., 2000). CSNB, Leber congenital amaurosis (LCA), and complete achromatopsia are three types of congenital retinal dystrophies that overlap clinically, as all patients present in early childhood with visual impairment and nystagmus.

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Test Details

  • Nonprogressive difficulty seeing in low light, existing from birth
  • Reduced visual acuity, myopia, and occasionally nystagmus and strabismus
  • Asymptomatic mothers with affected sons (X-linked inheritance)


4 weeks
2-5 mL Blood - Lavender Top Tube
Buccal Swabs

*Reporting times are typical, but could be extended in situations outside GeneDx's reasonable control.


81404x1; 81479x1
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**The CPT codes provided are based on AMA guidelines and are for informational purposes only. CPT coding is the sole responsibility of the billing party. Please direct any questions regarding coding to the payer being billed.


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