09/01/2025
𝗘𝘆𝗲 𝗗𝗶𝘀𝗲𝗮𝘀𝗲 & 𝗦𝘄𝗲𝗱𝗶𝘀𝗵 𝗩𝗮𝗹𝗹𝗵𝘂𝗻𝗱𝘀:
𝑊ℎ𝑎𝑡 𝑊𝑒 𝐾𝑛𝑜𝑤 𝐴𝑏𝑜𝑢𝑡 𝑅𝑒𝑡𝑖𝑛𝑜𝑝𝑎𝑡ℎ𝑦,
𝑎𝑛𝑑 𝐻𝑜𝑤 𝑊𝑒 𝐺𝑜𝑡 𝐻𝑒𝑟𝑒
One of the more interesting but challenging aspects of purebred dogs is understanding the health conditions that can arise in certain breeds. For Swedish Vallhunds, a spitz breed with heritage back to the Vikings, one of the biggest health concerns has been an eye disease known as retinopathy. Over the past 20+ years, researchers, veterinarians, and breeders have worked together to trace this condition from its first observations to a clear understanding of its genetic cause.
It’s important to remember that eye disease (and inherited disease in general) can occur in any dog, purebred or mixed. The difference with purebred populations is that we have the advantage of pedigree analysis and genetic studies. These allow researchers to trace how a disease is inherited and give breeders the tools to limit its spread in future generations. Far from being a weakness, this structured record-keeping is one of the greatest strengths of the purebred community when it comes to protecting the health of our future dogs.
𝐖𝐡𝐚𝐭 𝐄𝐲𝐞 𝐈𝐬𝐬𝐮𝐞𝐬 𝐇𝐚𝐯𝐞 𝐁𝐞𝐞𝐧 𝐒𝐞𝐞𝐧 𝐈𝐧 𝐕𝐚𝐥𝐥𝐡𝐮𝐧𝐝𝐬?
Veterinary ophthalmologists have reported several different findings in Vallhund eyes. None of these conditions are unique to Swedish Vallhunds - they are all health issues that can be seen in any dog. The difference is that in Vallhunds, careful tracking has allowed us to notice patterns and study them more closely.
🔹 𝑃𝑒𝑟𝑠𝑖𝑠𝑡𝑒𝑛𝑡 𝑝𝑢𝑝𝑖𝑙𝑙𝑎𝑟𝑦 𝑚𝑒𝑚𝑏𝑟𝑎𝑛𝑒𝑠 (𝑃𝑃𝑀): small threads of tissue left over from development in the eye.
🔹 𝐷𝑖𝑠𝑡𝑖𝑐ℎ𝑖𝑎𝑒: extra eyelashes that may irritate the eye.
🔹 𝐶𝑎𝑡𝑎𝑟𝑎𝑐𝑡𝑠: cloudy spots in the lens that can grow and cause blindness.
🔹 𝑉𝑖𝑡𝑟𝑒𝑜𝑢𝑠 𝑑𝑒𝑔𝑒𝑛𝑒𝑟𝑎𝑡𝑖𝑜𝑛: changes in the gel that fills the eye.
🔹 𝐶ℎ𝑜𝑟𝑖𝑜𝑟𝑒𝑡𝑖𝑛𝑎𝑙 𝑠𝑐𝑎𝑟𝑠: patches of scarring at the back of the eye.
🔹 𝑹𝒆𝒕𝒊𝒏𝒐𝒑𝒂𝒕𝒉𝒚 / 𝑷𝒓𝒐𝒈𝒓𝒆𝒔𝒔𝒊𝒗𝒆 𝑹𝒆𝒕𝒊𝒏𝒂𝒍 𝑨𝒕𝒓𝒐𝒑𝒉𝒚: regeneration of the retina that can progress to blindness.
Of these, the most serious in Swedish Vallhunds has proven to be retinopathy, since it can lead to complete blindness in some dogs. The retina is a thin, delicate layer of tissue that lines the inside of the back of the eye. Think of the eye like a camera: the lens focuses light into the eye, and the retina is like the film that captures the image.
𝐓𝐡𝐞 𝐓𝐢𝐦𝐞𝐥𝐢𝐧𝐞 𝐨𝐟 𝐃𝐢𝐬𝐜𝐨𝐯𝐞𝐫𝐲
🔹 𝐋𝐚𝐭𝐞 𝟏𝟗𝟗𝟎𝐬: With advances in technology, veterinarians in Finland and Sweden begin noticing unusual retinal degeneration in Vallhunds. The disease doesn’t look quite like PRA seen in other breeds.
🔹 𝟐𝟎𝟎𝟔–𝟐𝟎𝟎𝟕: Dr. András Komáromy (University of Pennsylvania) documents eye exam findings from Vallhunds in the US and Scandinavia. He reports early signs like pigment spots and mottled retina, progressing to retinal thinning and sometimes blindness. This raises suspicions of an inherited form of PRA.
🔹 𝟐𝟎𝟏𝟏: A collaboration between Professor Hannes Lohi (University of Helsinki) and Dr. Komáromy expands the study. Large pedigrees are built, hundreds of blood samples are collected, and clinical exams in the US, Finland, and Sweden confirm the disease is progressive and likely genetic. Known PRA genes from other breeds are excluded, pointing to something unique to Vallhunds.
🔹 𝟐𝟎𝟏𝟒: Two major papers are published. Researchers identify that Vallhund retinopathy is linked to abnormal expression of a gene called MERTK, which is already known in human medicine as a cause of certain types of retinal degeneration. They find that Vallhunds with retinopathy often have higher activity of this gene in their retinal tissue.
🔹 𝟐𝟎𝟏𝟕: The breakthrough: researchers discover that the likely cause is a LINE-1 insertion (a type of mobile DNA element) within an intron of the MERTK gene. This disrupts normal regulation of the gene and causes the retina to degenerate over time. This discovery allows the development of a DNA test by Animal Health Trust in the UK, and more informed breeding choices to be made.
𝐇𝐨𝐰 𝐃𝐨𝐞𝐬 𝐭𝐡𝐞 𝐃𝐢𝐬𝐞𝐚𝐬𝐞 𝐏𝐫𝐨𝐠𝐫𝐞𝐬𝐬?
🔹 𝐒𝐭𝐚𝐠𝐞 𝟏 (𝐦𝐢𝐥𝐝): Red or brown discoloration in the retina, sometimes seen as early as 2 months, but often noticed around age 4 or older. Dogs usually still see normally.
🔹 𝐒𝐭𝐚𝐠𝐞 𝟐 (𝐦𝐨𝐝𝐞𝐫𝐚𝐭𝐞): Retinal thinning, often becomes visible around age 6. Some dogs may begin to show night-blindness.
🔹 𝐒𝐭𝐚𝐠𝐞 𝟑 (𝐬𝐞𝐯𝐞𝐫𝐞): By around age 12, some Vallhunds with this disease can be nearly or fully blind, with severe day- and night-vision loss.
Progression is highly variable. Some affected dogs show changes early in life, while others only display mild signs even in old age.
𝐖𝐡𝐚𝐭 𝐃𝐨 𝐁𝐫𝐞𝐞𝐝 𝐂𝐥𝐮𝐛𝐬 𝐑𝐞𝐜𝐨𝐦𝐦𝐞𝐧𝐝?
Around the world, Vallhund breed clubs recommend a combination of DNA testing and regular eye exams (by board-certified veterinary ophthalmologists). DNA testing identifies whether a dog is clear, a carrier, or at high risk (homozygous for the mutation). Eye exams track whether the retina shows signs of disease, especially important in dogs that are affected by the mutation.
Because the mutation is relatively common in the breed, eliminating all carriers would severely shrink the gene pool. Instead, most breed clubs recommend responsible breeding strategies. This means carriers (dogs with one copy of the mutation) can be bred, but only to clear-tested dogs - and dogs with two copies of the mutation should generally not be bred, as they have the highest risk of developing retinopathy and producing affected dogs in their litters.
𝐖𝐡𝐚𝐭 𝐂𝐚𝐧 𝐈𝐧𝐝𝐢𝐯𝐢𝐝𝐮𝐚𝐥 𝐁𝐫𝐞𝐞𝐝𝐞𝐫𝐬 𝐃𝐨?
For breeders, the most important tools are genetic testing for MERTK retinopathy before breeding, and annual eye exams for breeding dogs. Making thoughtful pairing choices to avoid producing affected puppies, while still maintaining genetic diversity in the breed, will be key for the future of the breed. This means not excluding all carriers, but rather managing them carefully. For example, breeding a carrier to a clear-tested dog avoids affected offspring, while still preserving valuable traits overall.
𝐖𝐡𝐲 𝐓𝐡𝐢𝐬 𝐌𝐚𝐭𝐭𝐞𝐫𝐬, 𝐁𝐞𝐲𝐨𝐧𝐝 𝐕𝐚𝐥𝐥𝐡𝐮𝐧𝐝𝐬
The discovery in Swedish Vallhunds is not only important for the breed, but also for human medicine. The MERTK gene is known to cause incurable blindness in people, and studying how the disease presents in Vallhunds may contribute to new understanding and eventually new therapies for people too!
Thanks to decades of work by breeders, veterinarians, and researchers, we now have tools to identify at-risk dogs and to manage breeding responsibly. With careful testing and planning, we can better prepare to limit the appearance of this eye disease in future generations of Vallhunds.
𝐑𝐞𝐟𝐞𝐫𝐞𝐧𝐜𝐞𝐬 𝐚𝐧𝐝 𝐅𝐮𝐫𝐭𝐡𝐞𝐫 𝐑𝐞𝐚𝐝𝐢𝐧𝐠
Komáromy, A. M. (2006, 2007). Abnormal Findings in the Eyes of Swedish Vallhunds.
Komáromy, A. M., & Lohi, H. (2011). Update on Genetic Studies of Retinopathy in the Swedish Vallhund.
Cooper AE, Ahonen S, Rowlan JS, Duncan A, Seppälä EH, et al. (2014). A Novel Form of Progressive Retinal Atrophy in Swedish Vallhund Dogs.
Saija J Ahonen et al. (2014). Increased Expression of MERTK is Associated with a Unique Form of Canine Retinopathy.
Ahonen, S. J., Lohi, H., & Komáromy, A. M. (2014). Retinopathy in the Swedish Vallhund is Associated with Dysfunction of the MERTK Gene.
Richard Everson et al. (2017). An Intronic LINE-1 Insertion in MERTK is Strongly Associated with Retinopathy in Swedish Vallhund Dogs.
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