In a study published online in Genome Research (www.genome.org), researchers have identified a novel mutation in a gene associated with CRD in dogs, raising hopes that potential therapies can be developed for people suffering from these eye disorders.
CRD represents a heterogeneous set of disorders characterized by progressive loss of retinal cone function. As these photoreceptor cells allow us to see in bright light, loss of cones results in what is commonly known as dayblindness, and can advance to blindness altogether. Thus far, investigations into the genetic basis for autosomal recessively inherited cases of human CRD have turned up only a few genes associated with the disorder, therefore it is likely there are other genes associated with CRD not yet identified.
Eye disorders are one of the most frequently inherited disorders in dogs, however canine CRD is limited to only a few breeds. A gene mutation had previously been associated with CRD in the miniature long-haired dachshund, while a genetic basis for CRD in the standard wire-haired dachshund and the pit bull terrier remained unknown. In this study, scientists led by Dr. Frode Lingaas of the Norwegian School of Veterinary Science and Dr. Kerstin Lindblad-Toh of the Broad Institute of MIT and Harvard have identified a mutation in a novel gene for early-onset CRD in standard wire-haired dachshund by genome-wide association mapping of a dachshund family.
The genome-wide strategy utilized by Lingaas' group isolated a region on chromosome 5 associated with CRD in dachshund. A search for mutations of this area revealed that a portion of the nephronophthisis 4 (NPHP4) gene has been deleted and is likely responsible for recessively inherited CRD in the standard wire-haired dachshund. The finding is particularly interesting, as the human form of NPHP4 has been previously implicated in disease. "This gene has been associated with a combination of kidney and eye disease in human patients," explained Lingaas. "Here, we found a mutation that affects only the eyes, suggesting that this gene might be a candidate for human patients with eye disease only."
The researchers suggest that the protein coded for by the mutant form of NPHP4 may lack a domain that would normally interact with other proteins involved in eye function, yet still retain the region involved in kidney function. "The new information that the NPHP4 gene can be involved in eye diseases only can shed light on the etiology of some low-frequency eye diseases in people where similar mutations may be involved," Lindblad-Toh said.
Lingaas noted that identification of causal mutations for diseases has practical implications for dogs, as genetic tests could be implemented to avoid new cases of the disorder and reduce the frequency of the mutation in the population. Furthermore, this investigation of the genetic basis for CRD in dogs could facilitate the development of treatments for humans.
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