DNA Health testing

Golden Retriever

 

Our Golden Retrievers have been DNA tested for the following and copies of their results are included in our puppy/stud information pack:

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Ichthyosis (ICT)

Ichthyosis (ICT) is a condition resulting in flaky skin and dull hair, which can vary greatly between affected dogs. Dogs are generally otherwise healthy but do have a risk of skin infection.

An autosomal recessive condition caused by a mutation in the PNPLA1 (Type A) 

 

Progressive Retinal Atrophy Golden Retriever Type 1 (PRA-GR1)

Progressive retinal Atrophy, golden retriever 1 (GR-PRA1) is a late-onset inherited eye disease affecting golden retrievers. Affected dogs begin showing clinical symptoms related to retinal degeneration between 6 to 7 years of age on average, 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 called the Tapetum that can be observed on a veterinary eye exam. 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, eventually progressing to complete blindness in most affected dogs.

Genetic testing of the SLC4A3 gene in golden retrievers will reliably determine whether a dog is a genetic Carrier of GR-PRA1. GR-PRA1 is inherited in an Autosomal Recessive manner in dogs meaning that they must receive two copies of the mutated gene (one from each parent) to develop the disease

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Progressive Retinal Atrophy Golden Retriever Type 2 (PRA-GR2)

Progressive retinal Atrophy, golden retriever 2 (GR-PRA2) is a late-onset inherited eye disease affecting golden retrievers. Affected dogs begin showing clinical symptoms related to retinal degeneration at around 4 to 5 years of age on average, 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 called the Tapetum that can be observed on a veterinary eye exam. 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 in most affected dogs.

Genetic testing of the TTC8 gene in golden retrievers will reliably determine whether a dog is a genetic Carrier of GR-PRA2. GR-PRA2 is inherited in an Autosomal Recessive manner in dogs meaning that they must receive two copies of the mutated gene (one from each parent) to develop the disease.

 

Muscular Dystrophy Golden Retriever Type (MD-GR)

Golden Retriever Muscular Dystrophy (GRMD or just MD) is a sex-linked recessive disorder. A sex-linked recessive disorder means that the mutation occurs on the chromosome that determines sex (the X or Y chromosomes – XX codes for a female, while XY codes for a male). Dystrophin protein is required in order to connect muscles to bone, acting as an anchor for muscular cells.The mutation of the dystrophin gene is what causes a deficiency of dystrophin proteins in Golden Retrievers.

If the dystrophin gene has a mutation, this production is interrupted, leading to a reduced amount of dystrophin protein. The lack of dystrophin protein leads to the progressive degeneration of skeletal and cardiac muscles. The disease is similar to the human disease, muscular dystrophy.

Symptoms appear relatively quickly, at about six weeks to two months of age. A dog with muscular dystrophy will exhibit muscle weakness, difficulty standing or walking normally, and difficulty swallowing. Symptoms can range from relatively mild to severe, but GRMD is generally fatal by about 6 months of age.

The GRMD mutation is located on the X chromosome. Many sex-linked recessive diseases are located on the X-chromosome. Sex-linked recessive diseases typically affect males. This is because males inherit only one copy of the X chromosome (XY), while females inherit two copies (XX). This means that females will only ever inherit a single recessive copy of an affected gene (one X from mom and one X from dad). Because they have another X chromosome, they have a “second chance” in not displaying symptoms of the disease. The other X chromosome would have to be affected as well in order for them to display symptoms. Most females are carriers of the disease due to the low likelihood of an affected male and a carrier female breeding and producing a litter because of the fatality of the disease at a young age.

In contrast, a male that inherits only one copy of X does not have that “second chance.” A male receives one X from mom and one Y from dad. If the male inherits an affected X chromosome from mom, there is not another normal X chromosome that would replace the mutated gene. This means the male could inherit the affected X chromosome and will develop symptoms. So while both male and female dogs can be affected, GRMD is mostly a disease related to male Golden Retrievers. Females can be carriers of the mutation and will not exhibit any symptoms. A helpful website regarding sex-linked recessive disease inheritance can be found here.

It is important to genetically test female dogs to see if they are carriers of the disease. If a female carrier is bred, even to a male dog that does not have GRMD, there is a 50% chance per male puppy born that he will develop GRMD, which is fatal. There is a 50% chance that each female puppy born will also be a carrier and will not develop symptoms of GRMD. However, they now possess the ability to pass on GRMD to her offspring. It is a good idea to spay any female golden retrievers with GRMD (especially if they’re a common household pet) in order to prevent any accidents that could occur outside the home.

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Neuronal Ceroid Lipofuscinosis 5 Golden Retriever Type (NCL5-GR)

Neuronal ceroid lipofuscinosis (NCL) is a group of progressive degenerative diseases of the central nervous system. Signs of disease in affected dogs begin between one and two years of age and include behavior issues such as: anxiety, constant circling, aggression, compulsive behaviors, and loss of learned skills. Additional neurological symptoms include: tremors, ataxia (lack of coordination), localized and generalized seizures, and visual impairment occasionally to the point of blindness. The progressive nature of this disease often results in euthanasia of the affected dog by 3 years, due to the poor quality of life.

In Golden Retrievers, a two base pair deletion in the ceroid lipofuscinosis neuronal protein 5 (CLN5) gene is thought to cause this disease. This two base pair deletion (denoted as c.934_935delAG) causes a frameshift in the gene product that results in a shortened protein (p.E312Vfs*6). The shortened protein is predicted to lack 39 amino acids including those that are essential for proper processing and trafficking of the protein. Specifically, there are several glycosylation sites in this protein that are required for it to be transported to the correct part of the cell where it normally functions to degrade proteins (lysosome). It is hypothesized that lack of normal CLN5 results in abnormal accumulation of storage material particularly in the cells of the central nervous system, leading to disease.

NCL is a recessive trait, meaning two copies of the variant must be present, one inherited from each parent, for the dog to show symptoms. Based on the study that identified this mutation, the allele frequency for the CL allele is rare in the Golden Retriever population (less than 1%). If only one copy is inherited (from either parent), no symptoms will be observed but the animal is a carrier and can pass the variant to its offspring. If two carriers are bred together, each puppy born has a 25% chance of developing NCL.

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Progressive Retinal Atrophy (PRA-PRCD)

Progressive retinal Atrophy, progressive Rod-cone degeneration (PRA-prcd) is a late onset, inherited eye disease affecting many breeds of dog. PRA-prcd occurs as a result of degeneration of both rod and cone type Photoreceptor Cells of the Retina, which are important for vision in dim and bright light, respectively. Evidence of retinal disease in affected dogs can first be seen on an Electroretinogram around 1.5 years of age for most breeds, but most affected dogs will not show signs of vision loss until 3 to 5 years of age or later. The rod type cells are affected first and affected dogs will initially have vision deficits in dim light (night blindness) and loss of peripheral vision. Over time affected dogs continue to lose night vision and begin to show visual deficits in bright light. Other signs of progressive retinal atrophy involve changes in reflectivity and appearance of a structure behind the retina called the Tapetum that can be observed on a veterinary eye exam. Although there is individual and breed variation in the age of onset and the rate of disease progression, the disease eventually progresses 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.

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Sensory Ataxic Neuropathy (SAN)

Dogs with SAN begin to exhibit evidence of the condition between 2 to 8 months of age. However, many dogs with the genetic disease variant will never go on to develop clinical signs of the disease. In dogs with the disease variant that do develop clinical disease, the clinical signs appear insidiously, with affected dogs exhibiting ataxia and dysmetria. Decreased spinal reflexes and abnormal postural reactions are also seen, though they are not accompanied by muscle atrophy. Disease progression is slow but euthanasia is often elected while the dog is still a juvenile. SAN has only been found to cause disease in Golden Retrievers and when inherited through the maternal lines, and it should be noted that the variant is a risk factor meaning that not all Golden Retrievers with copies of the variant will go on to exhibit clinical signs.