HEALTH, DNA TESTING, AnD BREEDING PHILOSOPHIES
I have spent most of my career working in Small Animal Theriogenology (a reproductive science) specializing in Ovulation Timing, Cryopreservation, and Transcervical Insemination.
My philosophy with regards to how I make breeding choices is based on over a decade of selecting breeding stock, making breeding decisions and analyzing scientific data while working with a closed colony of “seeing eye” dogs. The goal at this particular facility was to try to make genetic gains in the area of health and trainability while reducing instinctive traits in an effort to improve the overall success rate. A lot of what I learned there, from consulting geneticists and other specialists, to trial and error, has been applied into my personal philosophy of breeding Maine Coons.
Health Screening for Genetic Diseases...
Most breeders I know are breeding Maine Coons to improve the breed, and although not everyone is breeding for the same reasons, most do a good job selecting the animals that are used for breeding. This includes running DNA tests, ultrasounds and x-rays to weed out animals that are affected and carriers of genetic diseases found in the Maine Coon breed.
However, please keep in mind that cats are NOT perfect creatures (and neither are breeders!). Having negative DNA results does not guarantee that the animal will never develop these diseases, it just means that they are less likely to. Also, some positive DNA tests traits are easily controlled through selective breeding. Open communication with your breeder is essential to understand what to expect health wise from your kitten, and what health guarantees are written into your contract should you have a problem down the road.
The main conditions that most breeders screen for are as follows:
HCM (Hypertrophic Cardiomyopathy) – DNA Test and Ultrasound(s)
HD (Hip Dysplasia) - X-Rays
SMA (Spinal Muscular Atrophy) – DNA Test
PKD (Polycystic Kidney Disease) – DNA Test
PKdef (Pyruvate Kinase Deficiency) – DNA Test
Always be sure to ask for DNA results from the breeder. A reputable breeder will readily share these results with you.
Other health conditions that warrant consideration:
Conditions related to Blue Eyes in White and Non-White Cats
High Coefficient of inbreeding (COI) and Inbreeding Depression
My Personal Breeding Philosophy Regarding Health Specifics...
Working at a Guide Dog School helping to choose breeding stock and evaluate the progeny instilled a very interesting perspective on health in me. I rank conditions, anomalies, and an animal’s carrier status on whether or not the condition is:
Life Threatening – Not Allowed in my Breeding Program.
Causes Financial/Physical Impact - Considered in my Breeding Program with Stipulations
Easily Controlled/Avoidable – Accepted in my Breeding Program
What follows is a brief definition of each condition listed above, the mode of inheritance (if known), followed by my personal philosophy about the condition. Please keep in mind that this is written from a scientific perspective, and does not take into consideration the emotional factors that these conditions can cause their owners.
HCM is a condition that produces increased left ventricular heart muscle wall thickness which decreases the hearts ability to function properly, resulting in sudden death. The mutation associated with increased risk for HCM in Maine Coons is called HCM1 - A31P (located on the MYBPC3 gene). DNA testing is available to test for this mutation. In cats that carry two copies of the mutation (homozygous) sudden death usually occurs by age 4 years. Cats that carry one copy of the mutation (heterozygous) have a longer life expectancy but are still at a higher risk of developing the disease. Again, keep in mind that having a negative DNA test result does not guarantee that your kitten will never develop HCM.
Another test that breeders can have conducted on their breeding stock is called an Echocardiogram. This is a medical imaging procedure performed by a Veterinary Cardiologist to evaluate the heart muscle.
I categorize HCM as a category #1 (life threatening) and do not accept carriers (homozygous or heterozygous) into my breeding colony.
From a genetic point of view, the mode of inheritance for HCM is not known at this time. According to UC Davis - Veterinary Genetics Laboratory, the A31P mutation does not appear to behave as a simple dominant trait, but more like a dominant trait with incomplete penetrance. Cats with one copy of the mutant allele are 1.8 times more likely to develop HCM than cats carrying normal alleles. Cats with two copies of the mutant allele are 18 times more likely to develop HCM than cats with normal alleles, and 10 times more likely to develop HCM than cats with one copy of the mutant allele.
If you are interested in more information on this disease, or links to the studies that have been published, you can find an excellent article written by Britta Singethan on the YankeeCats website here:
Spinal Muscular Atrophy:
SMA is an inherited neurodegenerative disorder that causes an ongoing loss of nerve cells in the lower spinal cord. This condition varies in severity from an unsteady gait to complete paralysis over time. There are no treatment options and no cure for this disease, though the condition does not seem to cause the animal pain.
The mode of inheritance for SMA is Autosomal Recessive. This allows the mutant gene to be easily controlled. Through strategic, selective breeding between carrier-cats and non-carrier cats, important lines are retained and the breeds gene-pool remains preserved. Here is an explanation of SMA DNA results, and how it affects your breeding outcomes:
N/N = This result means that the cat is neither affected with SMA, nor a carrier. If bred to another N/N animal, 100% of their offspring will neither be affected nor carriers of this disease.
N/SMA = This result means that the cat is not affected with SMA, but it does carry one copy (heterozygous) of the mutant gene. If bred to a N/N cat, approximately 50% of the offspring will be carriers, and 50% will be non-carriers.
SMA/SMA = This result means that the cat is affected with SMA. They carry 2 copies (homozygous) of the mutant gene and if bred to a N/N cat will produce 100% carrier cats. offspring. Note: If an affected cat is bred to a carrier cat N/K, 50% of the offspring will be affected, and 50% will be carriers. If bred to another affected cat, all resulting progeny will be affected.
Pyruvate Kinase Deficiency:
Pkdef is an inherited deficiency in the enzyme Pyruvate Kinase which impairs the red blood cells ability to metabolize. This leads to anemia and can result in symptoms such as lethargy, weakness and weight loss.
The mode of inheritance for PKdef is Autosomal Recessive. This allows the mutant gene to be easily controlled. Through strategic, selective breeding between carrier-cats and non-carrier cats, important lines are retained and the breeds gene-pool remains preserved. Here is an explanation of PKdef DNA results, and how it affects your breeding outcomes:
N/N = This result means that the cat is neither affected with PKdef, nor a carrier of PKdef. If bred to another N/N animal, 100% of their offspring will neither be affected nor carriers of this disease.
N/K = This result means that the cat is not affected by PKdef, but it does carry one copy (heterozygous) of the mutant gene. If bred to a N/N cat, approximately 50% of the offspring will be carriers, and 50% will be non-carriers.
K/K = This result means that the cat is affected with PKdef. They carry 2 copies (homozygous) of the mutant gene and if bred to a N/N cat will produce 100% carrier cats. offspring. Note: If an affected cat is bred to a carrier cat N/K, 50% of the offspring will be affected, and 50% will be carriers. If bred to another affected cat, all resulting progeny will be affected.
My personal philosophy on PKdef is that carrier-cats (heterozygous) can be bred to non-carrier cats, as long as the resulting kittens are DNA tested before being placed. Carrier kittens can be placed as pets and never enter the breeding program.
Hip Dysplasia (HD) is a disease of the hip joint in which one or both hip joints do not sit as deep in the acetabulum as they should. It is suspected to have a polygenetic mode of inheritance, meaning that it takes multiple genes to express the condition. Since these genes have not been identified, breeders have very little control over it and cannot predict the outcome. HD free parents can produce kittens with hip dysplasia, and cats affected with hip dysplasia can produce kittens without hip dysplasia. I have personally seen OFA (Orthopedic Foundation for Animals) excellent dogs bred to OFA excellent dogs produce an entire litter of dysplastic offspring. As breeders, the only thing we can do is screen our animals to make sure we are not breeding from affected animals. This does not guarantee that kittens will be free of hip dysplasia, but it is our hope that doing this lowers the risk of hip dysplasia. I have spoken with geneticists who feel that by the selective breeding of animals with good hips to animals with good hips, we are only burying traits which will pop up again at a later time. However it is the only tool that breeders currently have at their disposal.
I categorize this condition #2 – causing financial impact, as this condition typically requires surgery to correct but is not life threatening. I x-ray my breeding stock after one year of age and send the x-rays in to OFA (Orthopedic Foundation of America) to be graded. My philosophy is to use breeders whose hips fall into the acceptable breeding range based on OFA's recommendations. Since the genetic mode of inheritance is still unknown, cats producing this anomaly in their offspring are evaluated and considered for retirement from the breeding colony based on their breeding health record.
Patellar Luxation is where the kneecap luxates, or pops out of place. The suspected main causes are trauma, congenital defects or genetics. If caused by physical trauma (such as a broken bone or injury to the stifle joint caused by jumping/falling/landing abnormally) the clinical signs of a luxating patella will become suddenly evident. If, on the other hand, the cause is a congenitally /genetically inherited defect, the signs will slowly emerge and gradually evolve into lameness as the affected cat grows older.
Congenital malformations are thought to be caused by teratogens which interfere with normal fetal development (such as chemicals, infections, drugs or other environmental factors) but could also be hereditary in nature. It is thought that many cases of congenital patellar luxation have an hereditary component, but this has not been studied in detail. As with hip dysplasia, it is likely that this is a polygenic disorder (several genes involved) and that dietary, lifestyle and environmental factors will also be involved. Since these multiple genes have not been identified, breeders have very little control over it and cannot predict the outcome. As breeders, the only thing we can do is screen our animals to make sure we are not breeding from affected animals. This does not guarantee that kittens will be free from patellar luxation, but it is our hope that doing this lowers the risk.
I categorize this condition #2 – causing financial impact, as this condition typically requires surgery to correct. In cases such as these where the condition is not life threatening, my breeding philosophy is to evaluate all offspring of my breeding cats for potential problems. This can be difficult as information is gathered solely through owner notification. Since the genetic mode of inheritance is unproven, cats producing this anomaly in their offspring are evaluated for retirement from the breeding colony.
Entropion is a condition where the eyelid (usually lower) rolls inwards causing irritation and pain. Not much is known regarding the genetic mode of inheritance, though some suspect there is a familial predisposition. Empirical data lean towards other causes including re-occurring eye infections like Conjunctivitis (caused by bacterial infections such as Mycoplasma or viruses like Feline Herpes Virus) injuries, and head conformation such as eye shape, short muzzles and wider heads (brachycephalic). Some people think that the likely suspect is conformation, and that it can be easily controlled by choosing breeding partners that have larger, rounder eyes and longer muzzles.
I categorize this condition #2 – causing financial impact, as it typically requires surgery to correct which can run upwards of $1000+ depending on where you live and the degree of severity. In cases such as these where the condition is not life threatening, my breeding philosophy is if a breeding cat is of exceptional type and temperament, it remains in the breeding colony until the genetic mode of inheritance is proven. If he/she produces entropion in their offspring, then they are retired from the breeding colony.
Conditions related to Blue Eyes in White and Non-White Cats:
It is a common misconception that all white cats with blue eyes are deaf. This is not the case. Inherited deafness in all white cats is caused by the variable penetrance of the dominant white masking gene (simply known as “W”) which suppresses both pigmentation and hearing. The “W” gene appears to have complete penetrance over coat color, but incomplete penetrance for blue eyes and deafness. The cause of this variable penetrance is not known, but it suspected that other genes and/or environmental factors may be linked.
Maine Coons can have blue eyes for other reasons as well. If the cat has inherited the coat pattern of a pointed cat (such as a Siamese or Himalayan, for example) then blue eyes could be the result of these genes. Blue eyes in cats other than white/with white are not in accordance with the Maine Coon breed standard.
Another condition worth mentioning is Waardenburg Syndrome. Although few studies have been done regarding this condition in cats, this syndrome has been found in other species such as humans, dogs, minks and mice. This syndrome typically expresses bright blue eyes, areas of depigmentation (or white patches) in non-white cats, and some degree of hearing loss.
All white cats with either one or two blue eyes should be tested BAER tested for deafness before they are accepted into the breeding colony.
Polycystic Kidney Disease:
FIP and Inbreeding Depression: