A distinctive form of congenital stationary night blindness with cone ON-pathway dysfunction

Night blindness and abnormal cone electroretinogram ON responses in patients with mutations in the GRM6 gene encoding mGluR6

“…There was no delay in responses to light decrements such as dark spots appearing against the same background (38). These findings bring to mind a previous study of our patient 274-011 that found a much smaller delay (Ϸ20 msec) in responses of the occipital cortex to light increments, but not to light decrements, as measured by visual evoked responses (18). However, upon presenting a simultaneously appearing pair of white and black letters to another of our patients (063-007), there was no relative delay in the perception of either the white letter (i.e., a luminance increment) or the black letter (a luminance decrement).…”

“…Some of the clinical findings in one of the three patients with GRM6 mutations (274-011) have been reported previously (18). Here, we summarize and expand on these initial findings and describe those found in the other two patients.…”

“…However, two of our patients with GRM6 mutations had greater reductions of a-wave amplitudes than are typically seen in the complete form of X-linked night blindness (18); further investigations of additional cases are necessary to determine whether this finding would clinically distinguish patients with GRM6 vs. NYX mutations. Like the GRM6 patients, the NYX patients have residual rod responses that are possibly mediated through the gap junctions with cones (57).…”

Control of late off-center cone bipolar cell differentiation and visual signaling by the homeobox gene Vsx1

“…Although a number of genetic abnormalities of the ON visual pathway have been reported (20,(29)(30)(31)(32)(33)(34), the effect of the loss of Vsx1 function reported here is the initial description of a heritable OFF visual pathway-specific abnormality. Our findings suggest that the mild subclinical reduction in the ERG b͞a-wave ratio observed in humans with dominant VSX1 missense mutations (18) is the result of OFF-CB cell dysfunction that reflects the incomplete terminal differentiation of these cells.…”

Clinical Psychophysical Assessment of the ON- and OFF-Systems of the Magnocellular and Parvocellular Visual Pathways

“…There are many retina and eye diseases that could affect the gross function of MC and PC pathways [17][18][19][20][21][22][23][24][25] or diseases that produce selective impairment in ON-or OFF-systems such as as melanomaassociated retinopathy [18], X-linked retinitis pigmentosa [26], congenital stationary night blindness [27,28] and Duchenne Muscular Dystrophy [29].…”