Primary Lens Luxation

Other Names: Lens luxation, PLL
Affected Genes: ADAMTS17
Inheritance: Autosomal Incomplete Dominant
Mutation: chr3:40782144 (canFam3): G>A

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Common Symptoms

Primary lens luxation is an inherited abnormality of the eye affecting miniature bull terriers. It is characterized by dislocation of the lens in the eye due to the breakage of the ligaments (called zonules) that hold the lens in place. The age of onset is variable depending on whether a dog has one or two copies of the Mutation, but affected dogs typically present between 2 to 8 years of age with sudden signs of eye irritation. Symptoms of lens luxation include excessive blinking, squinting and tearing of the eye. Dislocation of the lens can occur in both the forward and backward position within the eye, but dislocation in the forward position is more common and serious. If not treated immediately, lens dislocation can lead to Glaucoma and vision loss.

Breed-Specific Information for the Miniature Bull Terrier

The Mutation of the ADAMTS17 gene associated with primary lens luxation has been identified in the miniature bull terrier. Though the exact frequency in the overall miniature bull terrier population is unknown, 49.2% out of 2137 miniature bull terriers tested had one copy of the mutation and 8.7% had two copies of the mutation, with an overall frequency of at risk dogs of 57.9%. Miniature bull terriers with two copies of the mutation typically show clinical signs between 4-5 years of age with all affected dogs showing clinical disease by 6 years of age. Miniature bull terriers with only one copy of the mutation typically show clinical signs at 6 years of age or older, but not all dogs with one copy of the mutation will develop disease within their lifetime. PLL has been reported in miniature bull terriers without this mutation, which suggests that other genes and/or environmental factors can play a role in the development of PLL in this breed.

Testing Tips

Genetic testing of the ADAMTS17 gene in miniature bull terriers will reliably determine whether a dog is a genetic Carrier of primary lens luxation. Primary lens luxation is inherited in an autosomal incomplete dominant manner in dogs meaning that dogs only need to inherit one copy of the mutated gene to be at an increased risk of developing the disease. Though lens luxation is most commonly seen in dogs having two copies of the mutated gene, carrier dogs have a low, but increased, risk of lens luxation. Thus, dogs that have one or two mutant copies of the gene are considered at-risk for lens luxation. When a carrier of this Mutation is bred with another dog that also is a carrier of the same mutation, there is risk of having affected pups. For each pup that is born to this pairing, there is a 25% chance that the puppy will inherit two copies of the mutation and a 50% chance that the puppy will inherit one copy of the mutation and, in either case, may be susceptible to lens luxation. Reliable genetic testing is important for determining breeding practices. Because symptoms may not appear until adulthood, genetic testing should be performed before breeding. In order to eliminate this mutation from breeding lines and to avoid the potential of producing affected pups, breeding of known carriers is not recommended. Miniature bull terriers that do not have the mutation have no increased risk of having affected pups when bred to a dog that is also clear for this mutation.

There may be other causes of this condition in dogs and a normal result does not exclude a different mutation in this gene or any other gene that may result in a similar genetic disease or trait.

References

  • Donner J, Kaukonen M, Anderson H, Moller F, Kyostila K, Sankari S, Hytonen M, Giger U, Lohi H. Genetic Panel Screening of Nearly 100 Mutations Reveals New Insights into the Breed Distribution of Risk Variants for Canine Hereditary Disorders. PLoS One. 2016 Aug 15;11(8):e0161005. [PubMed: 27525650]
  • 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 DR, Mellersh C. An ADAMTS17 splice donor site mutation in dogs with primary lens luxation. Invest Ophthalmol Vis Sci. 2010 Sep; 51(9):4716-21. [PubMed: 20375329]
  • Gharahkhani P, O’Leary C, DuffyD, Bernays M, Kyaw-Tanner M. Primary Lens Luxation in Australian Tenterfield and Miniature Bull Terriers is due to an old ADAMTS17 mutation and is an additive trait. Open Genomics J. 2012 Mar;5:7-13 DOI: 10.2174/1875693X01205010007. [Not in PubMed]
  • Gould D, Pettitt L, McLaughlin B, Holmes N, Forman O, Thomas A, Ahonen S, Lohi H, O’Leary C, Sargan D, Mellersh C. ADAMTS17 mutation associated with primary lens luxation is widespread among breeds.Vet Ophthalmol. 2011 Nov;14(6):378-84. [PubMed: 22050825]
  • PLL test results and statistics. [Internet]. 2010 [cited 7 April 2014]. Available at http://www.offa.org/stats_dna.html?dnatest=PLL.
  • Tzouganakis I, Tsvetanova A, Jeanes EC, Mellersh CS, Gould DJ. Investigation of the allele frequency of the G>A intron 10 ADAMTS17 mutation causing primary lens luxation in the Portuguese Podengo breed. Vet Ophthalmol. 2022 Jan;25(1):85-89. doi: 10.1111/vop.12960. [PubMed: 34870369]