Why is genetic health testing important?

The dog does not carry any copies of the mutant gene for the disease. It will never have the disease or pass the disease onto its offspring. Puppies are considered ‘clear by parentage’ for any particular genetic disease when both parents are clear for that same genetic disease. 

The dog has one copy of the mutant gene and one copy of the normal gene. It will not have and will not develop the disease.  This dog should only be bred to dogs clear of the same disease to prevent producing dogs affected by the disease. 

The dog has two copies of the mutant gene. It will have the disease and be affected by the disease at some point in its lifetime. Affected dogs should only be bred to clear dogs to ensure they produce no affected dogs; however, every pup produced of this pairing would be carriers of the disease. 

Autosomal Recessive: A pattern of inheritance in which an affected dog must have two copies of an abnormal gene in order to present with the disease or trait. 

Autosomal Dominant: A pattern of inheritance in which an 'affected' dog has one copy of a gene that contains a change or mutation and one normal gene on a pair of chromosomes. Offspring have a 50% chance of inheriting the disease-causing gene. 

Variable Expressivity: Refers to individuals who have the mutation, but their clinical presentation may vary from mild to severe. 

Autosomal Incomplete Dominant: Dogs only need to inherit one copy of the mutated gene to be at an increased risk of developing the disease.

Incomplete Penetrance: Not all dogs inheriting two copies (one from each parent) will display obvious physical characteristics. 

Progressive Retinal Atrophy, progressive rod-cone degeneration is a late onset, inherited eye disease affecting Labrador Retrievers. PRA-prcd occurs as a result of degeneration in the rod and cone photoreceptor cells of the retina, which are important for vision in both dim and bright light. Evidence of retinal disease can first be seen at around 1.5 years of age, however most affected dogs will not show signs of vision loss until 4 to 6 years of age. The rod type cells are affected first and dogs will initially have vision deficits in dim light (night blindness) and loss of peripheral vision. Over time, affected dogs lose night vision and begin to show visual deficits in bright light.  There is no cure for this disease and it will eventually lead to complete blindness in most dogs. 

Other inherited disorders of the eye can appear similar to PRA-prcd. Genetic testing may help clarify if a dog is affected with PRA-prcd or another inherited condition of the eye.

The recessive gene responsible for this disorder was identified at Cornell University. 

Though the exact frequency in the overall Labrador Retriever population is unknown, 10.3% out of 58 Labrador Retrievers from a population from the Czech Republic were carriers of the mutation and 1.7% were affected.

Inheritance: Autosomal Recessive

The D Locus  (Dilute) corresponds to the MLPH gene that is important in determining coat color in dogs. Mutations in this gene modify the expression of the pigments, resulting in a “dilution” or lightening of the coat color of dogs. Coat color determination is complex due to interactions of multiple genes responsible for both color and anatomic placement of the color. A dog with two mutant copies of the gene will have a diluted coat color that may be referred to as blue, charcoal, silver, Isabella or fawn (depending on the breed and the base coat color). 

Disease Association Note: Mutations of the D locus are sometimes responsible for a condition called color dilution alopecia (hair loss). The clinical presentation of alopecia associated with dilute coat color is variable within and between breeds; therefore, only a portion of individuals carrying two copies of the mutation (d/d) will show hair loss. Though two copies of the mutation (d/d) are necessary to develop color dilution alopecia, the variable presentation of this condition suggests that additional environmental or genetic factors contribute to the development of alopecia. The hair loss is caused by abnormal melanin storage in the hair, which leads to breakage of the hair shaft and the lack of normal regrowth of hair. Dogs with this condition can also be affected with recurrent bacterial skin infections originating in the hair follicles. Given that the modifying environmental or genetic factors responsible for alopecia are unknown, the only way to prevent color dilution alopecia is to not breed carriers or affected dogs. 

Other Names: Alopecia, Black hair follicular dysplasia (BHFD), Coat color dilution, Color dilution alopecia (CDA), Color mutant alopecia, D locus, d1 and d2 loci, Dilution gene

Inheritance: Autosomal Recessive

Stargardt disease is an inherited eye disease that affects dogs, primarily Labrador Retrievers. Onset of significant clinical signs is late in life, with affected dogs presenting with observable visual problems around 10 years of age. As with other retinal degenerations, such as progressive retinal atrophy, STGD is characterised by the degeneration of the rod and cone photoreceptor cells of the retina. Dogs therefore experience visual deficits in bright and low light conditions. It is a progressive disease and symptoms will get worse as the dog ages. 

Other Names: Juvenile Macular Degeneration, STGD

Inheritance: Autosomal Recessive 

Note: Stargardt Disease testing became available in early 2021.  It is estimated that over 30% of Labrador Retrievers are carriers or affected.  Although this is not a 'recommend' test, I highly encourage only getting puppies from breeders who test both the Sire and Dam. 

Congenital Myasthenic Syndrome (CMS) is an inherited Neuromuscular Disease affecting Labrador retrievers.  Dogs affected with CMS typically present around 2-3 weeks of age with severe exercise-induced weakness of all four limbs leading to collapse. Affected dogs will have decreased reflexes in all limbs and a short-strided gait that becomes more pronounced with exercise. Dogs may be humanely euthanized at a young age due to disease severity. Treatments used for a similar, acquired form of the disease known as myasthenia gravis, are ineffective for CMS. 

Inheritance: Autosomal Recessive 

Progressive retina atrophy, golden retriever 2 (GR-PRA2) is a late onset, inherited eye disease that can also affect Labrador retrievers. Affected dogs begin showing clinical symptoms related to retinal degeneration at around 4 to 5 years of age, though age of onset can vary. Initial clinical signs of progressive retinal atrophy involve changes in reflectivity and appearance of a structure behind the Retina. Progression of the disease leads to thinning of the retinal blood vessels, signifying decreased blood flow to the retina. Affected dogs initially have vision loss in dim light (night blindness) and loss of peripheral vision, progressing to complete blindness. 

Inheritance: Autosomal Recessive 

Progressive retinal atrophy, cone-rod dystrophy 4 is an inherited eye disease affecting dogs. 

PRA-crd4 occurs as a result of degeneration of both rod and cone cells of the retina, which are important for vision in dim and bright light. Affected dogs can show symptoms of vision loss or have signs of retinal disease by 3 years of age. However, age of onset varies significantly in PRA-crd4 affected dogs, and has been reported from 1 to 15 years of age. Although progression tends to be relatively slow, most affected dogs (especially those with an early age of onset) will progress to complete blindness. 

Inheritance: Autosomal Recessive with Incomplete Penetrance: meaning that not all 'affected' dogs develop clinical disease.  This suggests that other unknown genetic or environmental factors may play a role in modifying disease development and progression. 

Cone Degeneration (Labrador retriever type) is an inherited eye disease affecting Labrador retrievers. Affected dogs develop blindness in bright light (day blindness) and light sensitivity between 8 to 12 weeks of age.  Affected dogs have normal vision in low light and structures of the inner eye appear normal on eye exam. The cells responsible for vision in low light are not affected and thus, affected dogs will still be able to see normally in low light throughout their life. 

Other Names: Achromatopsia, Day blindness, Hemeralopia, Rod monochromacy 

Inheritance: Autosomal Recessive 

Canine Elliptocytosis is a rare inherited blood disorder. Normal red blood cells are round in shape but red blood cells in affected dogs appear oval-shaped and can have serrated edges. An affected dog may present with mild anemia and may be smaller than its littermates.  Elliptocytes can rupture more easily than normally shaped red blood cells. Though this does not normally cause problems in affected dogs, the risk of red blood cell rupture could become more severe if affected dogs have concurrent conditions that compromise cardiovascular health. 

Inheritance: Autosomal Dominant: Meaning one or two copies will cause an abnormal RBC shape. 

Hyperuricosuria is the excessive excretion of uric acid in the urine. This condition can cause the formation of stones in the bladder or kidneys (uroliths), which is uncomfortable and painful.  Clinical signs of HUU can include difficulty urinating, frequent urination, blood in the urine, and urinating in unusual places. Some affected dogs show no clinical signs. The stones are difficult to treat and often require surgical removal. The condition can become life threatening in males if the urinary tract becomes blocked.  HUU can occur in any breed.

Inheritance: Autosomal Recessive 

Myotubular Myopathy is an inherited muscle disease affecting Labrador Retrievers. Affected puppies are typically normal at birth, but between 7 and 19 weeks of age they present with muscle weaknes, decreased muscle mass, a hoarse bark and difficulty eating. Puppies are smaller than littermates, walk with a short, choppy gait and often fall over. The disease rapidly progresses from generalized muscle weakness and frequent episodes of collapse to a complete inability to stand or even raise their heads within 4 weeks of initial presentation.  While the disease is not painful, affected dogs are often euthanized between 3 and 6 months of age due to the rapid and severe progression of the disease.  

Other Names: X-linked myotubular myopathy, MTM1, XLMTM

Inheritance: X-Linked Recessive: This mutation has a sex-linked recessive inheritance pattern. Because males have only one X chromosome, this disease is expressed mainly in male dogs. 

*Females have two X chromosomes and must inherit two abnormal copies to be affected with this disease. Males have only one X chromosome and either have a normal copy of the gene or the mutation. 

Narcolepsy (Labrador retriever type) is an inherited disorder affecting Labrador retrievers.  The condition is caused within the nervous system resulting in suddenn collapse.  The condition produces a range of symptoms, some of the most common include: 

• Fainting 
• Collapsing
• Legs buckling
• Twitching
• Loss of reflexes
• Rapid eye movements
• Sleeping more during the day

Generally, episodes of the condition last a few seconds. Although some dogs can take a few minutes to fully recover from an episode.  The disorder is not usually life-threatening.  

Inheritance: Autosomal Recessive 

Pyruvate kinase deficiency (Labrador retriever type) is an inherited metabolic disease. Affected dogs have insufficient activity of the pyruvate kinase enzyme which breaks down glycogen for energy. Deficiency of this enzyme results in easily damaged red blood cells (hemolysis). Affected dogs typically present between 4 months and 2 years of age. Clinical findings include severe anemia, hardening of the bones, and an enlarged spleen and liver.  While dogs can live for several years with this disease, they typically die from severe anemia or liver failure by 5 years of age. 

Other Names: Pyruvate kinase deficiency of erythrocytes, PK 

Inheritance: Autosomal Recessive 

Copper toxicosis (Labrador retriever type) is an inherited metabolic disease resulting in chronic liver failure. Dogs with copper toxicosis have a decreased ability to excrete dietary copper from the body resulting in excessive copper storage in tissues and organs, including the liver, which can result in liver damage and subsequent cirrhosis. Though the age of onset and speed of disease progression are variable, most affected dogs will present in middle age with non-specific signs of liver dysfunction including weight loss, lethargy, weakness, vomiting, diarrhea, and abdominal pain. In late stages of disease, affected dogs may develop signs of liver failure including abdominal swelling, jaundice, and neurological dysfunction.  

Mutations of the ATP7A and ATP7B genes have been identified in Labrador retrievers; however, the exact frequency in the overall Labrador population is unknown due to lack of breeders testing &/or reporting the condition.

*Note: A mutation present in the ATP7A gene has been shown to decrease copper accumulation in dogs that have inherited one or two copies of the ATP7B gene mutation.  

Other Names: Copper Hepatoxicosis, Copper Storage Disease, Copper Storage Hepatitis, Menkes Gene Disease Modifier, Wilson Disease 

Inheritance: Complex Inheritance, meaning copper toxicosis in the Labrador retriever is a complex disease in which both genetic and environmental factors play a role.

The thyroid plays an important role in a dog's immune system and hormone balance.

Canine hypothyroidism is an inherited form of hypothyroidism that occurs in Labradors. Autoimmune lymphocytic thyroiditis is due to a deficiency of the hormones produced by the thyroid gland.  

Thyroid disease usually develops by the time the dog is 5 years old and symptoms include weight gain, lethargy and hair loss. 

Dogs are rated as normal, autoimmune thyroiditis, or idiopathically reduced thyroid function. 

Only 'normal' dogs should be used in breeding programs.  

Many inherited eye disorders have already been discussed above.  I felt it worth mentioning that there are other inherited disorders associated with eyelids that are minor in nature. There are no DNA screening tests for the below: 

Entropion: The eyelashes are turned inward in.  

Ectropion: The eyelashes are turned outward.  

Distichiasis:  The eyelashes develop in an abnormal location, emerging from the eyelid margin rather than the eyelid skin. 

These conditions can be corrected with minor surgery.  

Seizures in Labrador Retrievers can be due to an inherited form of epilepsy.  However, seizures are often a result of a wide variety of non-genetic factors.  Infections, trauma, low blood sugar levels, toxins and pesticides exposure can result in seizures.  Fortunately, this disorder is rare and many dogs respond well to medication; however, this condition can be life-threatening as well.

There is no screening test for the inherited form of epilepsy.