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Sealyham SIGHT Registry FAQs

Updated 9/10/06
For more information, please contact:
George Packard
Director, GDC
What is the SIGHT registry?
SIGHT is a database for all Sealyham Terriers where owners can register their dogs, as well current eye exams, pedigree and other significant information. The information is currently available by request in the form of reports and genetic pedigrees showing family groups of dogs. SIGHT is run by GDC (Institute for Genetic Disease Control).. For an article describing the registry, download
"Lily's Story: the Push to Control Lens Luxation in Sealyham Terriers" (Acrobat PDF)

What is GDC?
GDC is a not-for-profit organization established in 1990 to help breeders reduce the prevalence of genetic diseases in dogs..

What does the registry have to do with the Sealy DNA test research?
SIGHT is working closely with the lens luxation DNA research project at the University of Missouri to help locate family groups of dogs whose DNA is important to the project.

What is the purpose of the registry?
The main purpose of SIGHT is to help breeders make breeding decisions that will reduce the prevalence of lens luxation. The goal of SIGHT is to register as many Sealys as possible, including every known affected dog and its relatives. When a breeder know s that a dog is affected she can estimate the risk that other relatives may have for carrying or passing on the defective gene.

Why should I register my dog with SIGHT?
The effectiveness of the registry is directly dependent on how complete it is. Since lens luxation is a late-onset disease, we can never be certain that a dog is free of the disease. That’s why we urge every owner to register their dogs and then update their registrations with yearly eye exams. In addition, as more dogs are registered, we will be able to contact registered owners whose dogs appear to be at greater risk for lens luxation as suggested by new information in the data base.

Could my dog develop lens luxation if neither parent has it?
If both parents carry the defective gene there is a very high probability that some of the puppies will be affected. A dog may carry the defective gene and show no symptoms of the disease.

What’s the simple version of the genetics of lens luxation?

  • Both parents and all offspring of an affected dog will be carriers;
  • The parents and all offspring of a carrier have a 50 percent chance of being carriers;
  • A carrier must be mated with another carrier to produce an affected;
  • A carrier will always pass the defective gene to some of its offspring;
  • Without a gene test, we cannot prove that a dog is NOT a carrier.

How does the genetics of lens luxation work?
Researchers believe that lens luxation is an autosomal recessive trait. There is probably one key gene involved in lens luxation, and a dog must inherit that gene from both parents to be affected with the disease.

Lens luxation is what is called a “late onset” disease. It generally occurs in Sealys between age 4 and 8. A dog who is a carrier may have been bred many times before one of its offspring shows symptoms, and that is what makes the disease very, very difficult to control.

If a dog carries only one copy of the gene, that dog is called a carrier, and will not show the trait. A carrier will pass along copies of the gene to some of its offspring each time it is bred. A fairly simple rule of genetics gives the probabilty for how many puppies in a litter will carry the gene, but there is no way to know which individuals are the carriers.

When both parents carry the gene, another rule of genetics predicts that some of the puppies will inherit copies of the genes from both parents, and will be affected. Several others will inherit just one copy of the gene from one parent and will be carriers. And the remaining puppies will not inherit copies of the gene at all.

Without a DNA test, the only way we know a dog is a carrier is if it has produced an affected offspring.

The parents of an affected dog, in the case of lens luxation, are assumed to be carriers. If a dog is a carrier, but has many excellent traits, that dog can still be bred, but only under strict guidelines. The dog must not be bred to another carrier, and every one of the dog’s offspring must be presumed to be a carrier until proven otherwise, either by a DNA test, or by several test breedings to a known carrier which produce no affecteds.

How will breeders use the registry to help reduce the risk of lens luxation?
If enough dogs, including affected dogs, from a particular family group are registered, GDC can create a genetic pedigree of that group. The genetic pedigree shows clearly where the affected dogs are in the family, and with that knowledge, the breeder can determine which dogs are probably carriers, and what the carrier risk is for other dogs. GDC will provide information, resources and access to canine genetic counselors to help breeders with complex risk assessments and breeding questions.

What is a genetic pedigree?
A traditional pedigree shows the parentage back through three or more generations. If you take a traditional pedigree and begin filling in the rest of the close relatives (siblings, half-sibs, offspring, multiple matings, etc.), you’ve got the beginnings of a genetic pedigree. The genetic pedigree can include 75-100 or more dogs and shows the relationships among them as graphical chart. If enough closely related dogs are registered, the genped provides a comprehensive picture of the location of affected and carrier dogs in a family. With that information breeders can make risk assessments about breeding any two dogs.

Why doesn’t the registry just publish a list of affected dogs?
Focusing on affected dogs without information about the dogs’ close relatives is of very little value over the long run for breeders. The key to making good breeding decisions is being able to estimate carrier risk in the relatives of an affected dog. In addition, exclusive listing of affected dogs tends to create a “witchhunt” atmosphere among breeders. Cooperation and sharing of information is crucial in the fight against a genetic disease. That’s why SIGHT only releases information on family groups of dogs and provides guidelines for how breeders can use that information.

How prevalent is lens luxation among Sealyham Terriers?
We do not have an accurate estimate of the prevalence for lens luxation in the breed. We continue to collect enough reports about affected dogs to know that without an immediate and comprehensive effort to stop the spread of the gene, the problem could become much worse than it is now. As we gather more information in the SIGHT registry we are finding that a significant percentage of Sealys are probably carriers of the defective gene.

Why don’t we just stop breeding to carriers?
First of all, we can only confirm that a dog is a carrier if it has produced an affected offspring. Without a gene test, we can only estimate the carrier risk of dogs who are related to affected dogs. And just because a dog has not produced an affected offspring does not in any way ensure that it is not a carrier.
Second, the Sealyham gene pool is very small, and removing carriers from the breeding program may also remove many of the good traits that are essential to the breed. In simple terms, if we have a Sealy who has many good traits but is a known carrier, we need to find a mate for that dog who has good traits as well, but has a very low carrier risk. And we must inform buyers of the risk, and track the health of all puppies for the rest of their lives.

How do I register my dog?
The SIGHT application gives step by step instructions. We encourage a CERF eye exam by an ophthalmologist or a basic eye exam by a veterinarian, but it is not required for SIGHT registration.

How much does it cost to register?
There is no charge for registering a dog affected with lens luxation or a dog that is an assumed carrier of the gene (must have produced affected offspring). The first-time registration is $10 per dog. Subsequent updates with new eye exams are $5. The rates are reduced for registering several related dogs at the same time.

Does my dog need an eye exam every year?
No eye exam is required for SIGHT registration.
We strongly urge owners to have yearly exams for their dogs, particularly if the dog is at risk for lens luxation. It is extremely important to catch the disease in the early stages when there may still be some chance of saving the dog’s eyes.. SIGHT will send reminders to owners to have a lens luxation exam by an ophthalmologist.
ACVO Clinic List (Locate a veterinary opthalmologist in your state)

Why should I register my dog if it doesn’t have lens luxation?
Until we have a 100% accurate DNA test, we cannot say for certain that any particular dog is not at risk.

Will SIGHT certify my dog as being clear of lens luxation?
Not at this time. When a 100% accurate DNA test is available, SIGHT will then be able to certify the genotype of a dog.

Can I provide a blood sample for DNA research without registering?
At this point the research laboratory at the University of Missouri is only needing blood samples from affected dogs, their parents and grandparents, their siblings, and their offspring along with the second parent (the affected dog's mate). Blood sample submission is confidential and you do not need to register with SIGHT to donate a sample. Blood Sample Submission Form

I’m confused about where to send the application forms.
Always send the eye registration forms to GDC, PO Box 177, Warner, NH 03278. If you are submitting a blood sample send copies of the forms to the University of Missouri research lab as well. See the application for details.

Why does SIGHT emphasize registering complete litters?
It is extremely important to record every dog in a litter because we cannot know for sure which dogs may develop the disease. If one dog in a litter isn’t recorded, and that dog has lens luxation, the registry will not be able to identify carriers in that line, and may provide inaccurate risk assessments.

Why is SIGHT an "open" registry?
An open registry provides all evaluation information (negative and positive) on a dog to users of the registry. Breeders must know which dogs are affected in a family group in order to lower the risk of producing more affected dogs, while at the same time preserving those good traits that they consider valuable in a dog or its line.

Can I register but keep my dog’s eye evaluation private?
SIGHT is an open registry. All information is available to any Sealyham owner who has also registered a dog with SIGHT. Owners who register their dogs agree to make health information in the registry available to other users of the registry. Keeping information about a dog with lens luxation from other breeders is essentially a guarantee that the defective genes will continue to be spread throughout the breeding population.

Will the registry really help reduce the prevalence of lens luxation?
Using an open registry to select against a single recessive trait is effective if a significant number of dogs are registered, and if breeders follow a proven methodology for making breeding decisions based on the information in the registry. There are a number of documented cases where intensive projects such as the SIGHT registry have significantly reduced the prevalence of single-gene and even multiple-gene disease within several generations of dogs. For more information, see "Control of Canine Genetic Diseases," by Dr. George A. Padgett (Howell Book House).

We must be cautious, however, because the mode of inheritance of lens luxation has not been proven. At this point researchers strongly believe that the disease is simple autosomal recessive and that it involves a single gene. We are proceeding on that assumption.


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