Post date: May 23, 2011 6:55:23 PM
The research carried out on UK Mini Long-haired Dachshunds using clinical and ERG testing has now been published in the Veterinary Opthalmology journal (Volume 14, Issue 3, May 2011). The authors are from the Animal Health Trust (AHT):
Claudia Busse
Keith C. Barnett
Cathryn S. Mellersh
Vicki J. Adams
Objective To investigate ophthalmic and cone-derived electrodiagnostic findings in outbred Miniature Long-haired Dachshunds (MLHD) homozygous for a mutation in the RPGRIP1 gene previously associated with cone-rod dystrophy 1 (cord1).
Animals A total of 36 MLHD homozygous for the RPGRIP1 mutation and 23 dogs clear of the mutation (control group).
Procedures The dogs underwent ophthalmic examination and photopic electroretinogram (ERG) recordings.
Results None of the control dogs presented with clinical or ophthalmic signs consistent with cord1. Amongst the dogs homozygous for the mutation one presented with bilateral symmetrical total retinal atrophy. None of the other dogs in this group showed signs consistent with cord1. Photopic ERG recordings were available in 23 control dogs and 34 dogs homozygous for the mutation. Photopic a- and b-waves following four light stimuli (3 cdS/m2) at a rate of 5.1 Hz were not significantly different between groups. The amplitudes of the 30 Hz flicker (128 flashes, 3 cdS/m2) response were significantly reduced in the dogs homozygous for the PRGRIP1 mutation. The difference in age between the two groups did not significantly affect the difference.
Conclusion Homozygosity of the RPGRIP1 mutation does not invariably result in early onset cord1. However, cone derived ERG recordings show evidence of a reduced cone or inner retinal function in homozygous but clinically normal MLHD. Modifying genes that have yet to be identified may influence an individual dog’s risk of developing the blinding cord1 and also the age of onset and rate of progression.
In plain English...
The publication is intended for the veterinary profession, therefore many of the terms may not mean a lot to the layman. There's nothing particularly enlightening about the results that we were not already aware of, but they do show that retinal signals are statistically reduced in dogs homozygous for the cord1 mutation ("Affected"): i.e. "Affected" dogs have reduced quality of vision even though they may appear clinically normal.
Interestingly, if an ophthalmologist were only to look at the reduced ERG output observed in the homozygous affected dogs without looking at a control comparison, then they would be considered as clinically normal.
The AHT has more recently confirmed they are close to isolating the second mutation which is believed to influence the age of onset of PRA.
The full title of this latest paper is: