Why is health testing so important, and what is CHIC?
Inherited diseases fall into two broad classes: simple and complex.
1. Simple inherited diseases are the result of mutation of a single gene and represent around 70- 75% of the known inherited diseases in the dog. The mutation may be recessive or dominant. If recessive, then a dog has to inherit the recessive mutation from both parents before it is clinically affected; a dog that has one recessive mutant gene version and one normal gene version is a clinically normal carrier. If a dog inherits a dominant mutant gene from either of its parents it will usually be clinically affected despite having a normal copy of the relevant gene. Often, individual breeds, or related breeds, will have a predisposition to these simple, single gene disorders, although even in predisposed breeds, the prevalence of the disease is usually, but not always, low.
2. Complex inherited diseases are often described as multifactorial because they involve the inheritance of a number of different mutant genes, that is, they are polygenic, and the clinical expression of these mutant genes can be altered by environmental influences. These complex diseases give rise to clinical conditions that worry breeders the most, diseases like hip and elbow dysplasia, epilepsy and heart disease. These complex diseases rarely show breed specificity and are seen across many different breeds as well as being described in both cross breed and mixed breed populations, often at prevalences akin to those seen in pure breed populations.
Some inherited conditions only become apparent at later stages in a dog’s life.
One other important consideration is that not all inherited conditions are congenital, i.e. present at birth. It should also be remembered that not all congenital conditions
are inherited.
Sometimes the clinical consequences of an inherited disease do not become apparent in an affected dog until late in the dog’s life, and these late onset diseases present real challenges to the dog breeder because a dog could be well past its reproductive phase, and have been bred from, before it’s clinically affected state is recognised.
What can breeders do?
Breeders of pure bred dogs have a real opportunity to address these inherited diseases and reduce their prevalence, because it is the breeder that decides which sire is to be mated to which dam to produce a litter of puppies. It is thus possible, where screening schemes are available, for breeders to screen all of their potential breeding stock for signs of these inherited diseases, before they are bred from, and then use the results to formulate breeding programmes to reduce the prevalence of the diseases in future generations. Putting all of the potential breeding stock through these health screening schemes gives breeders a better understanding of the kind of genes a particular dog carries and therefore what it is likely to pass on to its offspring. Armed with this information breeders can avoid mating two dogs that have an increased chance of producing clinically affected puppies.
What is CHIC?
The Canine Health Information Center, also known as CHIC, is a centralized canine health database sponsored by the Orthopedic Foundation for Animals (OFA). CHIC, working with participating parent clubs, provides a resource for breeders and owners of purebred dogs to research and maintain information on the health issues prevalent in specific breeds by establishing a recommended protocol for breed specific health screening and recognizing dogs tested in accordance with that protocol
CHIC also maintains a DNA Bank that collects and stores canine DNA samples along with corresponding genealogic and phenotypic information to facilitate future research and testing aimed at reducing the incidence of inherited disease in dogs.