I just received the following additional email from Ann:
"...I probably should add that I am also very concerned that we do not over select against Goldens with ichthyosis. This is one of the first genetic tests we have available and we know that roughly two thirds of Golden Retrievers of European lines and a significant number of American Golden Retrievers will be either affected or carriers. We also know that in American Goldens, at this time, the most frequent manifestation may be dandruff. While it is reasonable to use the test to guide the breeding of ichthyosis carriers and affected Golden Retrievers, we will undoubtedly soon have genetic tests for diseases that are far more serious than ichthyosis (e.g SAS). I believe that it is important that our gene pool remains diverse and we do not narrow it in an attempt to eliminate the gene for ichthyosis just because we have a test for this gene.
Ann F. Hubbs DVM, PhD ...."
And the response from Rhonda Hovan (GRCA Health committee, AKC Health committee):
"...As Ann mentioned, we're not aware of any GI manifestations of the gene identified as causing ichthyosis. However, the wide variation in expression of the disease among dogs tested as affected indicates that there is still much we don't know about ichthyosis. Factors that cause these differences by modifying gene expression could be another gene, but more likely are epigenetic. Epigenetic factors include all environmental exposures, beginning prenatally. Further, it is also likely (based on early data in dogs but lots of data in humans) that many GI symptoms are also influenced by epigenetic factors, beginning prenatally.
This leads to two ways that ichthyosis and GI disorders can be associated other than by heritable genes. First, they may share environmental factors that increase the expression of each disease. An example of this from humans is that it is now known that the microbiome (the total inventory of all the microbial communities found throughout the body) is altered when a baby is born by C-section instead of vaginally. This is believed to be the cause of elevated rates of GI disorders, asthma, allergy, and many other conditions associated with birth by C-section. In humans, therefore, some children will express both GI disorders and asthma -- but the connection is an epigenetic exposure that increases the risk for expression of each condition, rather than a genetic link.
A second way that two diseases can be linked epigenetically is that expression of one disease can trigger changes in the body that increase expression of the other disease. Again using an example from humans, we know that obesity causes low-grade inflammation that often persists for decades. This inflammation is part of the pathway that leads, over time, to other diseases such as cardiovascular disease, cancer, and diabetes. So most of us have heard that obesity is linked to cardiovascular disease, cancer, and diabetes, and in part that link can be traced to the underlying inflammation caused by obesity.
All in all, your observation is very interesting, and thank you for bringing this to our attention! There is certainly much we don't know yet about ichthyosis, so it's important to take things slowly, because rushing to remove the gene from the population has the potential to harm genetic diversity and lead to greater problems down the road.
Finally, Purina did a wonderful article on this topic a few months ago, attached. This will also appear in the next GRNews, but you are welcome to share it by email too since many people on the various Lists may not be GRCA members. And you have my permission to forward and cross-post my email too.
and a link to the article by Purina Research: