The STCA developed a Web-based, Relative Risk Analysis Calculator to help breeders perform their own analysis of the relative risks associated with their breeding options. The Relative Risk Analysis Calculator is designed around Dr. J. Bell's work on CA. The calculator can be used for any autosomal recessive disorder. This page provides an introduction and basic instructions on how to use the calculator.
Most readers are probably already familiar with the STCA's On-line Pedigree Search site. This site has been hosted on the STCA Website for several years now and contains a large database of Scottish Terrier pedigrees. Mary O'Neal started the project and continues to add more records to the database each month. Although this site and the associated database does not replace the official AKC Stud Book and STCA Pedigree Search site does offer breeders and other followers of the fancy the ability to look up pedigree information that is based on the AKC Stud Book and other public records.
The STCA Pedigree Search site can also be used to investigate prospective "Trial" breeding options. By selecting a candidate stud dog and brood bitch, users can develop a pedigree for prospective offspring from the breeding. Another option that is available within the Pedigree Search site is called "Breeding Info." By clicking on this option for any dog in the database, users can find out information about littermates, siblings, and any offspring that the dog may have as the result of recorded breedings
All of the dogs that are listed in the CA Affected Database have a link to their record in the STCA Pedigree Search site. By using the various options available in the Pedigree Search site, users can locate dogs that are related to CA Affected Scotties and then use the Risk Analysis Calculator to assess the risks associated with many breeding options.
Please follow along with the following example to see how the Relative Risk Analysis Calculator can be used to help investigate the risks associated with a specific breeding. The calculator provides information predicting breeding risks for single autosomal recessive disorder. It does not work other types of disorders such as sex-linked disorders or dominant mutations. It does not provide calculations for multiple disorders simulataneously.
Step 1. Open A Trial Breeding Pedigree
For this example, two dogs are being reviewed: CH Eowyn Singer Of Simple Songs X Gryndlscot Miss Represented. The owners on both dogs have given their permission for us to discuss this trial breeding of a dog with no known risks for CA with a bitch that is a full sibling to an affected.
To begin, [Click Here] to open a Trial Breeding pedigree for CH Eowyn Singer Of Simple Songs X Gryndlscot Miss Represented. The Trial Breeding pedigree should have opened in a new window so that you can look at it carefully and then return to this page. Also note that the request was set to a 6 generation pedigree so that it will match the Relative Risk Calculator.
Step 2. Identify CA Risk Factors
Introduction to Risk Factors:
To analyze the Relative Risk associated with the off-spring from a proposed breeding, one must identify what is currently known about the parents, siblings, grand parents, etc. The dogs are assigned the following risk factors:
Dogs listed in the CA Affected Database as clinically diagnosed with CA
The direct parents of those dogs listed above as Affected
Full Siblings to Affected Dogs
Other dogs from the same litter as an Affected Dog or a repeat breeding of the same parents
Full Siblings to Carrier Dogs
Other dogs from the same litter as a Carrier Dog or a repeat breeding of the same parents
STCA Pedigree Search Site Risk Codes:
Data from the CA Registry Database has recently been added to individual records in the STCA Pedigree Search database. Each dog that has been clinically diagnosed as Affected with CA has been tagged within the Pedigree Search database with a *A* symbol after their registration number. In a similar manner, the parents (Sire & Dam) of each affected Scottie has been identified with a *C* symbol after their registration number. Finally, full siblings of these dogs have been identified with either a *SA* or *SC* after their registration number.
Please note that these FOUR risk codes are the only codes that the Relative Risk Analysis calculator uses. The codes have been assigned to individual records in the Pedigree Search database through a careful process of reviewing the Pedigree for each affected Scottie and the Breeding Info for their Sire and Dam.
Periodic updates will be made to the Pedigree Search database to add any new CA Risk Codes. Users should always check the latest entries in the CA Affected Database and then check the Pedigree Search site to determine if the Risk Codes have been added or not.
Risk Codes in the Trial Breeding Pedigree
Look at the Trial Breeding Pedigree for CH Eowyn Singer Of Simple Songs X Gryndlscot Miss Represented and notice that the bitch has a *SA* code after her registration number. This code indicates that she is the Full Sibling of an affected. As such, she has a specific risk for carrying the recessive gene that produces CA. Notice also that both of her parents have the *C* code for an Obligate Carrier after their registration number. When recording Risk Codes, it is not necessary to enter all of the risk codes. In this case, the SA code for the Dam is all that we need to record. The C codes for both grand parents are "behind" the dam's risk code and will be ignored by the Risk Calculator. So the general rule is that once a code has been identified, it is not necessary to look for any more codes further back in the pedigree.
Step 3. Use the Relative Risk Assessment Calculator
Dr. Bell's article on Relative Risk Assessment offers the following pedigree and presents the calculations leading to the Affected Risk and Carrier Risk results. This pedigree shows two Great Grandparents with CA Risk factors -- one bitch on the Sire side is a full sibling to a carrier (e.g. *SC*) and another bitch on the Bitch side is a full sibling to an affected (e.g. *SA*) dog. These two dogs are the only ones with an identified risk factor.
Let's see how the Relative Risk analysis calculator can be used to handle these calculations. To start, please [Click here] to open the STCA Relative Risk Analysis calculator in a new window. If possible, it may help to arrange the two windows so that they are both visible, otherwise it will be necessary to switch back and forth between the two browser windows. A graphic image of the Risk Calculator is show below.
Fig. 1 Relative Risk Analysis Calculator (Click on the image for a larger view)
To demonstrate how to use the Relative Risk Assessment Calculator, enter SC for the first GreatGrandDam and SA for the third GreatGrandDam. (These entries are identified by the two circles in the graphic to the left.) Please note that you can simply type over (replacing) the text that is already in these cells. Also note that the * symbols are not used in the calculator. The graphic to the left also shows that the analysis results are located towards the bottom of the table.
If you've entered the two Risk factor codes properly, the calculator will display the same results as shown above.
Go ahead and experiment by entering risk codes in different places and see how the results change. All calculations are automatic and update as soon as you input new codes.
Once you are satisfied that you understand how to enter the Risk Factor codes, you can either delete the entries or reload the page to prepare for another pedigree.
Risk Analysis of our Trial Breeding Pedigree
If you have not done so already, please [Click here] to open the STCA Relative Risk Analysis calculator in a new window. If you have been experimenting with the Risk Calculator, please click on the Reset button. Our Trial Breeding pedigree has only one Risk Code on the Dam's side of the pedigree, so enter SA as the code for the Dam. As mentioned earlier, it is not necessary to enter the two C codes for the Grand Parents on the Dam's side. The results section near the bottom of the Risk Calculator window will change to indicate Affected Risk = 0 % and Carrier Risk = 33.5 %.
Notice that the Sire's side of the pedigree has no known Risk Factor codes. One cannot say that the dog has no risk, just that his risks a completely unknown.
A Trial Breeding Pedigree will display CA Risk Codes in the 2nd and 3rd generations only. Notice that the registration number field is not displayed for any of the dogs in the 4th, 5th or 6th generations. To check all of these dogs for risk codes, it will be necessary to go back to the main Search page and open a regular pedigree window. The most effective procedure for doing this is as follows:
Print a copy of the Trial Breeding Pedigree.
Go to the main Search page and open a 4-generation Pedigree for the Sire. This pedigree will display the same information as our Trial pedigree.
Click on each of the four dogs in the 3rd generation to open a new pedigree. Each of these pedigrees will display the Risk Codes we need for the 4th, 5th and 6th generations in our initial Trial Breeding pedigree; so record any Risk Codes on the printed copy of the Trial Pedigree.
As you finish each pedigree, use the "Back" button to return to the Sire's pedigree.
Repeat these steps for the Dam's pedigree.
Once all of the Risk Codes have been recorded on the Trial Pedigree, transfer them to the Relative Risk Calculator.
Dr. Bell's article on Pedigree Risk Analysis states that the risk calculations will give you the relative risk of producing a genetic defect for an individual Scottie. The On-line Relative Risk Analysis Calculator can be used to analyze these risk factors without doing the math.
To improve your chances of NOT producing either an Affected or a Carrier dog, you would want to choose a breeding (among several options) that has the lowest risk factors.Statistics and probabilities are not a guarantee, and until we have a DNA Test for a genetic condition there will always be some risk associated with any breeding.
Additional Background Material:
Users who are interested in reviewing additional material that explains how the Relative Risk Analysis Calculator works can select either of the following links. Please [Click Here] for a PowerPoint briefing on how the Risk Calculator works. This version of the briefing does require ActiveX components that may not be compatible with all computer security settings. The PowerPoint slides are clickable so you can move forwards and backwards through the slide. There is no script with the version. Or [Click Here] for a strictly web page based version of the briefing. This version of the briefing uses screen capture images of the slides, includes a script to accompany the slides and does not require any ActiveX Components or the PowerPoint application.
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