Day blindness is an autosomal recessive condition which, in affected dogs, causes blindness under bright light conditions, despite having normal vision in dim light. This condition is caused by a progressive degeneration of cone photoreceptors in the retina in young dogs. Day blindness in the dog is similar to total colour blindness in humans, which is caused by mutations in the cyclic nucleotide gated channel beta-3 (CNGB3) gene. Two mutations of this gene have been identified in dogs with day blindness, a nucleotide change in exon 6 in German Shorthaired Pointers and an entire gene deletion in Alaskan Malamutes. Therefore, it was previously thought that these were the only cause of this genetic condition.
However, in a recent investigation, researchers have found that day blindness shows genetic heterogeneity, meaning that many different mutations can cause this condition. In this study it was found that while most Australian Alaskan Malamutes affected by day blindness had a mutated (deleted) CNGB3 gene sequence, there were some that had a non-mutated CNGB3 gene sequence. Also, no significant nucleotide substitutions or deletions were observed between the CNGB3 gene sequences of the affected and unaffected dogs, suggesting no affect on the protein’s function. This therefore suggests that deletion of the CNGB3 gene is insufficient to explain all day blindness cases.
However, in a recent investigation, researchers have found that day blindness shows genetic heterogeneity, meaning that many different mutations can cause this condition. In this study it was found that while most Australian Alaskan Malamutes affected by day blindness had a mutated (deleted) CNGB3 gene sequence, there were some that had a non-mutated CNGB3 gene sequence. Also, no significant nucleotide substitutions or deletions were observed between the CNGB3 gene sequences of the affected and unaffected dogs, suggesting no affect on the protein’s function. This therefore suggests that deletion of the CNGB3 gene is insufficient to explain all day blindness cases.
Further research into the genetic causes of this condition is obviously warranted in order to improve breeding and the quality of life of many dogs.
Primary Source:Seddon, J.M., Hampson, E.C. G. M., Smith, R.I. E. and Hughes, I.P., 2006, Genetic Heterogeneity of day blindness in Alaskan Malamutes. Animal Genetics 37, 407-410.
Abstract available at: http://www.ingentaconnect.com/content/bsc/agen/2006/00000037/00000004/art00022
For more day blindness information:
http://www.alaskanmalamute.org/Health/dayblind.asp
http://www.malamutehealth.org/articles/eye_dayblindness.htm
Pictures sourced from:
http://largedogbreedz.com/gallery/displayimage.php?album=40&pos=0
http://www.allpetsnetwork.com/b/alaskan-malamute.shtml
http://www.alaskanmalamute.org/Health/dayblind.asp
http://www.malamutehealth.org/articles/eye_dayblindness.htm
Pictures sourced from:
http://largedogbreedz.com/gallery/displayimage.php?album=40&pos=0
http://www.allpetsnetwork.com/b/alaskan-malamute.shtml
Posted by:
Megan Weller 29/5/08
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