Primary Lens Luxation (PLL) in Dogs: Breeds at Risk, Inheritance, and DNA Testing
Primary Lens Luxation can cause sudden, severe, and permanent blindness from glaucoma. In at-risk breeds, DNA testing before breeding is essential.
Primary Lens Luxation (PLL) is an inherited condition where the zonular fibers that suspend the lens in the eye break down, causing the lens to fall out of its normal position (luxate). A displaced lens can block fluid drainage, causing dangerously elevated pressure (glaucoma) and rapid, irreversible blindness.
What Happens in PLL
Normal eye: The lens is held in place by thousands of tiny fibers (zonules) in the center of the eye, allowing it to focus light on the retina.
In PLL: The zonules are structurally abnormal due to a ADAMTS17 gene mutation. They break down over time, usually between ages 3-8 years, causing the lens to:
- Subluxate (partially displace) — early stage
- Luxate anteriorly (fall forward into the anterior chamber) — the most dangerous stage
- Luxate posteriorly (fall backward into the vitreous) — less immediately dangerous
Anterior luxation is the emergency. The displaced lens blocks the drainage angle of the eye, causing intraocular pressure to spike rapidly. Without emergency treatment (typically surgical lens removal or eye removal), blindness and severe pain result within 24-72 hours.
Breeds Most Affected
PLL has been documented in numerous breeds. Highest prevalence:
- Terrier breeds (Jack Russell Terrier, Rat Terrier, Miniature Bull Terrier, Tibetan Terrier, Lancashire Heeler)
- Wire Fox Terrier and relatives
- Chinese Crested
- Shar Pei
- Australian Cattle Dog
- Miniature Schnauzer
The ADAMTS17 mutation has been identified in over 40 breeds and mixed-breed dogs.
Inheritance
PLL caused by the ADAMTS17 mutation is autosomal recessive with incomplete penetrance in heterozygotes:
| Result | Status | Risk |
|---|---|---|
| N/N | Clear | No PLL risk from this mutation |
| N/PLL | Carrier/At Risk | Low risk (possibly 20%+ may develop PLL — incomplete penetrance) |
| PLL/PLL | Affected | High risk of developing PLL; most will be affected by middle age |
Critical note: PLL is NOT fully recessive in the traditional sense. Dogs with ONE copy of the mutation (Carrier/Heterozygous) have some risk of developing PLL — though significantly lower than two-copy dogs. This makes PLL different from purely recessive diseases like CNM or EIC where one copy causes no disease.
Breeding Implications
Because Carriers (one copy) have elevated PLL risk themselves, breeding decisions are more complex than for purely recessive diseases:
- Clear × Clear: No PLL offspring from this mutation. Preferred.
- Clear × Carrier: 50% Clear, 50% Carrier offspring. Carrier offspring should be disclosed and monitored. Acceptable if Carrier parent is otherwise excellent and from health-tested stock.
- Carrier × Carrier: 25% Clear, 50% Carrier, 25% Affected. Produces two-copy dogs with high PLL risk. Avoid.
- Affected × anything: Not recommended for breeding.
Symptoms and Emergency Recognition
PLL most commonly presents in middle-aged dogs (3-8 years) as:
- Sudden pain (squinting, pawing at eye, sensitivity to light)
- Cloudy or blue-tinted appearance to the eye (corneal edema from elevated pressure)
- Red eye
- Sudden vision loss in one eye
Anterior lens luxation is a veterinary emergency. If a dog in an at-risk breed shows these signs, seek emergency veterinary care immediately — the window to save vision is measured in hours.
DNA Testing
DNA tests for PLL (ADAMTS17 mutation) are available from Optigen, Animal Genetics, Embark, and Paw Print Genetics. Testing is a cheek swab; results identify Clear, Carrier/Heterozygous, and Affected/Homozygous status.
For all breeds with known PLL prevalence, stud dogs should be tested and results disclosed. Even a Carrier result is important information for the dam owner's breeding decision.
Summary
Primary Lens Luxation causes lens dislocation and glaucoma, potentially causing sudden blindness in middle-aged dogs. It is caused by an ADAMTS17 gene mutation and affects numerous breeds, particularly terriers. Unlike purely recessive diseases, dogs with one copy (Carriers) have some risk of developing the disease. DNA testing is available and should be used in all at-risk breeds. Anterior lens luxation is a veterinary emergency. Breeding Clear × Clear is the safest approach; Carrier × Carrier should be avoided.