My dog only has one copy of the Primary Lens Luxation (PLL) variant, yet they are listed as At-Risk. Why is this?

The ADAMTS17 variant is responsible for an increased risk of Primary Lens Luxation (PLL). This causative variant has an additive inheritance type and not a recessive mechanism of inheritance. So while dogs with one copy of the variant have a higher risk than dogs with two healthy alleles at ADAMTS17, their risk is much lower than a dog with two copies of the variant. 

The actual risk associated with having one copy of this variant appears to vary in a breed-specific manner.

Because dogs with one copy of the variant can still develop Primary Lens Luxation (even if this risk is low), we use the term "At-Risk" instead of "Carrier."