Slow and fast rod ERG pathways in patients with X-linked complete stationary night blindness carrying mutations in the NYX gene

PURPOSE. To study the slow and fast rod signals of the scotopic 15-Hz flick er ERG in patients carrying mutations in the NYX gene, which has been recen tly identified as the cause of the complete form of congenital stationary n ight blindness, CSNB1. METHODS. Twenty eyes of 11 patients with CSNB1 who had nondetectable standa rd ERG rod b-waves were involved in the Study. Scotopic ERG response amplit udes and phases to flicker intensities ranging from -3-37 to -0.57 log scot opic trolands . sec (scot td . sec) were measured at a flicker frequency of 15 Hz. ERG signals to flicker intensities between -3.37 and -1-97 and betw een -1-17 and -0.57 log scot td . sec were considered to represent primaril y the slow and fast rod ERG pathway, respectively. Additionally, standard E RGS were performed. Twenty-two normal volunteers served as control subjects . RESULTS. For the slow rod ERG pathway, all patients exhibited ERG signals t hat were indistinguishable from noise. Accordingly, there was no systematic phase behavior for the slow rod signals. For the fast rod ERG pathway, the signals were significantly above noise, but they were significantly reduce d in amplitude and advanced in phase. CONCLUSIONS. There is evidence that the slow and the fast rod ERG signals c an be attributed to the rod bipolar-Ail cell pathway and the rod-cone- coup ling pathway, respectively. The current study provides evidence to suggest that a defective NYX gene product (nyctalopin) prevents detectable signal t ransmission through ON rod bipolar cells, but there is a residual transmiss ion through rod-cone gap junctions in CSNB1, possibly through the OFF cone pathway.