Eyes are the Prize: Identifying the Cause of Lens Luxation in Terriers
Certain breeds of dog are highly susceptible to a form of inherited eye disease known as primary lens luxation. Lens luxation occurs when problems with the structures that support the lens in the eye cause the lens to detach and move around. This is not only painful and directly damaging to the dog’s vision, it can also lead to glaucoma and other secondary vision problems.
Although lens luxation is seen in a wide variety of dog breeds – including numerous types of terriers, Australian Cattle Dogs, Chinese Cresteds, Chinese Shar Pei, and Border Collies – there are certain breeds in which the condition is particularly problematic. Lens luxation occurs in more than 1 out of every 6 Lancashire Heelers, and it has proved so damaging to Miniature Bull Terriers in the UK that there has been some discussion of breeding them back to standard Bull Terriers in order to reduce the disease’s frequency.
Identifying the gene, or genes, responsible for lens luxation in the various affected dog breeds could hopefully help breeders reduce the frequency and consequences of the condition. That’s why scientists Dr. David Sargan, from the University of Cambridge, and Dr. Gary Johnson, from the University of Missouri, teamed up to try and locate the source of the problem.
The scientists’ early efforts to locate the lens luxation gene in Minature Bull Terriers and Lancashire Heelers were hindered by the fact that lens luxation was simply too common in the two breeds. There wasn’t enough variation to be able to identify what gene(s) might be causing the disease, although they were able to narrow down the location in which the mutation had to occur. That was when, with the help of the AKC Canine Health Foundation, the scientists decided to move their research into a breed that had a lower frequency of lens luxation – Jack Russell Terriers.
Switching breeds worked, and the scientists discovered that the major cause of lens luxation in terriers seemed to be a mutation that caused transcription of a gene known as ADAMTS17 to be cut off too early – making a much shorter protein. Although the gene did not explain all cases of lens luxation in Jack Russell Terriers, Lancashire Heelers, and Miniature Bull Terriers – there was a small percentage of dogs of each breed that were affected without the mutation – it did seem to explain the excess risk.
Interestingly, a similar mutation in human ADAMTS17 has also been shown to lead to not only similar eye damage but short stature – causing a condition known as Weill-Marchesani syndrome (WMS). This has raised the question of whether selecting for smaller dogs may have contributed to increasing the frequency of lens luxation in affected terrier breeds, although a relationship between ADAMTS17 and skeletal size has not yet been demonstrated in dogs.
It will be fascinating to see how future research on both the human and canine conditions can be combined to give scientists an improved understanding of both ocular health and the complex interrelationships between the structures of the eye and the rest of the body.
This work was funded by AKC Canine Health Foundation Grants 2291, 567-A, 881-A & 747.
Farias, Fh, Johnson, Gs, Taylor, Jf, Giuliano, E, Katz, Ml, Sanders, Dn, Schnabel, Rd, Mckay, Sd, Khan, S, Gharahkhani, P, O'leary, Ca, Pettitt, L, Forman, Op, Boursnell, M, Mclaughlin, B, Ahonen, S, Lohi, H, Hernandez-Merino, E, Gould, Dj, Sargan, D and Mellersh, Cs (2010) An ADAMTS17 Splice Donor Site Mutation in Dogs with Primary Lens Luxation. Investigative Ophthalmology & Visual Science.
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