DNA Testing

It may sound peculiar that many practitioners of safe and sane feline husbandry would do DNA Testing on their cats.  We’ve even heard some people accuse breeders of having inferior or somehow flawed pedigrees and that is the reason they do DNA Testing.  This thought process is simply uninformed and ill advised.

One of the most important responsibilities that any conscientious breeder must do is make every effort to improve their cats’ health and longevity.  After many years of scientific study concentrating on feline diseases and genetic abnormalities, and discoveries of which genome strands are responsible for the development of more and more feline- and breed-related congenital defects, it becomes increasingly important for breeders to know the DNA make up of their cats and their pedigrees.

It is through increased awareness of the genetic make up of a breeder’s lines that we can take the steps necessary to eradicate these defects…a gargantuan task that only truly responsible breeders are even remotely interested in obtaining…and why it’s vitally important, even to the everyday pet owner, that they care about this issue also.

Like many species of animals (including human beings), genetic anomalies exist within the very basic fabric of life: our DNA.  As advances in research and technology move forward, discoveries on how DNA genomes relate to specific feline diseases have improved and become more accurate.  There is still much work to be accomplished in these areas, but what we have discovered needs to be integrated into a rich and diverse Maine Coon breeding program.

At present, the following congenital diseases are screened by responsible breeders, including a little background about each defect:

HCM (Feline Hypertrophic Cardiomyopathy):

This heart disease is probably the most common cardiac defect that is diagnosed in cats.  It is

characterized by a thickening of the muscular walls of the heart, causing enlarging and decreasing the efficiency of the heart’s pumping action.  It’s known as a silent killer because it typically crops up without warning, showing no obvious signs of onset at the beginning and most cat owners don’t regularly screen for its development.  According to University of California Davis scientific studies, the A31P genome is the marker on the DNA strand that indicates whether a Maine Coon cat is clear of possible complications in the future.  While the presence of this genetic defect doesn’t guarantee that the cat will develop HCM, it dramatically increases the chances that they will.

By DNA testing for this disease “breeders will be able to use this information to improve the vigor of the breed. A better understanding of test results will also contribute to a more realistic appraisal of the value of the test in breed improvement.” ¹

Sadly, because there is much that is still not understood about how this disease is actually triggered, the lack of this genetic marker is not a guarantee that HCM can’t develop.  This is the MAIN reason why knowledgeable Maine Coon breeders and owners should have their cats’ hearts scanned by a board-certified cardiologist who is very familiar with and understands HCM and what they are looking for.  Doing so will allow veterinarian intervention, if needed, to treat the disease early and extend your Maine Coon’s life, while keeping them as comfortable as possible for the duration of their lives.

PK Def (Erythrocyte Pyruvate Kinase Deficiency):

This blood disorder which usually manifests as severe anemia can cause lethargy, jaundice, enlargement of the abdomen and weight loss; there is no specific period in the cat’s lifespan that this can develop.  Genetically, it is most commonly found in twelve feline breeds, including Maine Coon cats.

Because this genome defect is an “autosomal recessive” genetic anomaly, it takes both male and female cats being a “carrier” for this disease to actually affect the kittens.  This means that when a PK Def heterozygous “carrier” (male OR female) mates with a homozygous “clear” or “non-carrier” cat, then there is a 50% chance that kittens could become a PK Def “carrier” (the remaining kittens would become homozygous “non-carriers”) HOWEVER none of the kittens would be in danger of developing PK Def.

Should a heterozygous “carrier” male AND a heterozygous “carrier” female mate, there would be a 25% chance that kittens would be “affected” and develop the disease, and a 25% chance that kittens would become homozygous “non-carriers” while the remainder of the litter would become heterozygous “carriers.”  It is this result that needs to be avoided.

Therefore, responsible breeders screen their cat’s DNA for this disorder in order to avoid a pairing of two heterozygous “carrier” cats that would be in danger of producing kittens who may develop the disease. To genetically eliminate the PK Def defect would be ideal, however there is very little risk to kittens born to a heterozygous/homozygous pairing.

Cats that are “carriers” are not at risk* of developing the disease in their lifetime.

*Since there are no absolutes in natural expression of genetic alleles, the scientific ratio factor for developing PK Def in the offspring of a heterozygous/homozygous pairing is noted as <1%.

SMA (Spinal Muscular Atrophy):

This insidious genetic defect is another autosomal recessive anomaly and appears to currently be unique to the Maine Coon cat breed.  The question of why only Maine Coon cats is currently a mystery.  At present, scientists have identified this defect as a deletion of parts of the LIX1-LNPEP gene on the A1 chromosome in the DNA strand.  The characteristics of the disease is expressed by increased instability, mostly in the hind-quarters and a tremor or inconsistent gait.  Advanced SMA causes muscular atrophy and loss of control of hind legs as the motor neurons of the spinal column cease to function.

The condition typically begins to manifest around the fourth or fifth month of the kitten’s life, however there have been cases of rare late-developing SMA in some patients.  Veterinarians who have studied this disorder report that cats who are afflicted with the disease do not feel pain and can live comfortable lives as indoor-only cats.

As with PK Def, it’s important to identify cats who are heterozygous (carrier) of the genetic defect to prevent pairing with another heterozygous Maine Coon cat, thus avoiding the manifestation of SMA in kittens.

PKD (Polycystic Kidney Disease)

PKD (or technically “PKD1”) has been around for a long time, mostly presenting in the Persian breeds.  How it began to creep into other breeds, including Maine Coon cats is unknown.  PKD is another inherited disease that usually begins by forming cysts on the kidneys around 12 months of age.  Renal failure typically follows later in life and because of the long span of time between cysts and renal failure, the two maladies were not thought to be related at first.  The fact that the disease doesn’t have a “strong clinical presentation…The presentation of PKD1 is similar to one of the most common causes of death for any cat, renal failure. Thus, PKD1 has gone unnoticed for many years…” ²

It is an autosomal dominant gene defect, therefore in many cases, a kitten or cat only needs ONE copy of the defect in order to develop PKD, and a positive PKD cat will produce at least 50% offspring as PKD positive, therefore should not be allowed to breed.

¹ UC Davis Veterinary Medicine, Veterinary Genetics Laboratory, “Maine Coon HCM,” https://www.vgl.ucdavis.edu/services/cat/MaineCoonHCM.php, February 10, 2018
² UC Davis Veterinary Medicine, Veterinary Genetics Laboratory, “PKD1 (Polycystic Kidney Disease) in Felines,” https://www.vgl.ucdavis.edu/services/pckd1.php, February 10, 2018