When the neighborhood feline floozy has a tryst with the local tomcat, the appearance, temperament, and health of their kittens is anyone’s guess.  On the other hand, planned breeding of purebred parents yields reasonably predictable results. Cat breeders depend on this predictability, and they choose the best animals possible, to improve a breed’s particular characteristics.  This predictability can come at a steep price, though: a higher risk for hereditary disorders.  

How can we improve a particular breed’s characteristics without passing along unforeseen genetic disorders?  This question is always on the minds of veterinarians, veterinary researchers, breeders, and geneticists.  Every year, we discover more answers.

It is now widely accepted that a genome map is an essential tool for the study of genetics in any species.  If you think of the genome (the genetic material) as the instruction manual for the creation and operation of the individual, then the genome map is analogous to the index.  Having this map allows the genome to be scanned quickly to identify areas where certain characteristics are located.  Once identified, they can be further scrutinized for more detailed study.  Although the mapping of the feline genome has not been greeted with the same fanfare as that surrounds the human genome project, it may prove to be nearly as important in the understanding and eradication of devastating genetic diseases.  After all, many genetic diseases in dogs and cats have almost exact parallels to genetic diseases in humans, and understanding the feline genome helps us understand genetic traits in humans too. 

Once the genes that cause disease have been identified, researchers attempt to develop tests that could distinguish affected (they have the disease), carrier (they have the defect, but appear normal), or clear (totally unaffected) animals.  Identifying carriers is of paramount importance, because cats can carry the gene for an illness and never show any clinical signs.  Without genetic tests, breeders may breed two animals that appear completely normal, yet produce sick kittens.  If genetic tests could be performed at birth or early in a cat’s life, breeders could scan their entire breeding stock, identify carrier cats with hidden genetic disorders, selectively breed to prevent the disease from appearing in future generations, eventually breeding out the most serious defects.  It would also allow pet owners to test their cat for the disease, even before any clinical signs develop, allowing for earlier medical or surgical intervention.  In the future, DNA tests might be able to predict the presence of defective genes even before birth, which would force breeders to confront some difficult ethical and economic issues.

Gene therapy is a novel approach for the treatment of diseases: the delivery of new genetic information. Although modifying an affected cat’s malfunctioning genes may sound like science fiction, it is already science fact. The idea behind gene therapy is to deliver and insert new DNA into a living organism.  Several hereditary diseases in cats and dogs have been treated by gene therapy, and studies are currently underway to use viruses to deliver the gene for the feline hormone erythropoietin.  This hormone increases the production of red blood cells. The ultimate goal of these studies is to provide a clinically useful therapy for anemic cats, especially those cats suffering from erythropoietin deficiency that commonly accompanies chronic kidney failure. Gene therapy can be administered directly into cells by the injection of DNA, or by encapsulating the DNA into little lipid droplets called liposomes.  Alternatively, cells that have been genetically altered in culture can be implanted into the recipient.  Despite the promise of gene therapy, concerns about safety and efficacy remain, as relatively little is known about the durability of the transferred genes, and the practicality of repeated gene therapy treatments.

Genetic research is a slow and expensive process.  Currently, only a few genes responsible for cat diseases have been discovered, mainly because the focus has been on finding the genes for inherited cat diseases that might serve as models for human disease.  Of the dozen or so feline disease for which the genes have been definitively identified, DNA screening tests exist for four of them.  The best candidates for study have been diseases caused by a single gene, as well as diseases that can be readily diagnosed via other diagnostic tests. Ultimately, the goal is to find the genes for some of the more common genetic disorders of cats, and then, if possible, eliminate a particular inherited disease altogether.  This is where breeders play a critical role.  It is only when breeders, veterinary researchers, and geneticists work together that genetic research can be successful.  Breeders provide pedigree information and DNA samples over several generations that offer the critical data needed to perform these kinds of studies.  While some breeders fear being associated with a genetic problem in their breed, the majority of conscientious breeders have been extremely willing to work with dedicated researchers on eliminating inherited illnesses.  As people who care about cats, breeders and researchers share a common objective: fewer homeless and more predictably healthy cats.  
 

Glossary 

Carrier – a cat that has the gene responsible for a disease, yet shows no signs of the disease itself.

Clear – a cat that does not have the gene responsible for a disease. 

Gene – a discrete section or region of DNA, located on a chromosome, that contains coding instructions or information.  Genes are transmitted from parent to offspring, and ultimately dictate what an individual animals inherited traits, such as appearance, eye color, etc. 

Genome – a complete copy of an animal’s DNA

DNA – deoxyribonucleic acid.  It is the molecule that carries the individual genetic code for all living animals.

Chromosome – thread-like strands of DNA that contain hundreds or thousands of genes.  Chromosomes come in pairs, and offspring inherit one of the paired chromosomes from each parent.

Updated 2/9/06