Primary Lens Luxation

Primary lens dislocation is the displacement of the lens from its usual position, either towards the anterior or posterior chamber of the eye, as a result of a mutation in the ADAMTS17 gene.

Symptoms

Clinical signs of primary lens dislocation appear at middle age, around 4 to 7 years of age. Symptoms common to this disorder include severe pain, tearing of the eye, decreased vision, clouding of the affected eye and redness. Displacement of the lens can cause an increase in intraocular pressure, which can lead to glaucoma. In some cases, lens dislocation may occur at the same time in both eyes.

Disease Management

Treatment of the disease will depend on whether the dislocation occurs in the anterior or posterior chamber, and on the presence of glaucoma. The main objective is to lower the ocular pressure and treat the underlying causes. In the case of anterior lens dislocation, surgical removal of the lens is used to try to save vision. Other options include glaucoma management, long-term use of eye drops for posterior chamber dislocations, or removal of the eyeball if there is pain.

Genetic basis

This disease follows an autosomal recessive mode of inheritance. Autosomal recessive inheritance means that the dog, regardless of sex, must receive two copies of the mutation or pathogenic variant to be at risk of developing the disease. Both parents of an affected dog must carry at least one copy of the mutation. Animals with only one copy of the mutation are not at increased risk of developing the disease, but may pass the mutation on to future generations. Breeding between dogs carrying genetic variants that can cause disease, even if they do not show symptoms, is not recommended.

Technical report

Primary lens luxation is a condition in which the lens is displaced from its usual position, causing symptoms such as pain, loss of vision and even glaucoma. A mutation in the ADAMTS17 gene has been identified as a possible causative factor for this disease in dogs. The ADAMTS17 gene belongs to the ADAMTS gene family, which encodes metalloproteases, enzymes with a structural function in the lens fibers of the eye. In a study by Farias et al. (2010), a specific mutation was identified in the ADAMTS17 gene (c.1473+1G>A) that caused a frameshift and the introduction of a premature termination codon. This variant was found to be significantly associated with the development of primary lens luxation in three breeds of dogs analyzed in the study: Jack Russell Terrier, Miniature Bull Terrier and Lancashire Heeler. Subsequently, this same mutation was identified in dogs with primary lens luxation but from breeds other than those mentioned above.

Most affected breeds

Australian Cattle Dog
Border Collie
Chinese Crested Dog
Chinese Shar-Pei
German Hunting Terrier
Jack Russell Terrier
Lancashire heeler
Miniature Bull Terrier
Parson Russell Terrier
Patterdale Terrier
Portuguese Podengo
Rat Terrier
Sealyham Terrier
Tenterfield Terrier
Tibetan Terrier
Toy Fox Terrier
Volpino Italiano
Welsh Terrier
Wirehaired Fox Terrier
Yorkshire Terrier

Bibliography

Farias FH, Johnson GS, Taylor JF,et al. An ADAMTS17 splice donor site mutation in dogs with primary lens luxation. Invest Ophthalmol Vis Sci. 2010 Sep;51(9):4716-21.

Gould D, Pettitt L, McLaughlin B,et al. ADAMTS17 mutation associated with primary lens luxation is widespread among breeds. Vet Ophthalmol. 2011 Nov;14(6):378-84.