Progressive Rod-Cone Degeneration, or PRA-prcd, is a form of Progressive Retinal Atrophy (PRA) in which the cells in the dog's retina degenerate and die. PRA for dogs is similar to retinitis pigmentosa in humans. Most affected dogs will not show signs of vision loss until 3-5 years of age. Complete blindness can occur in older dogs. Progressive Rod-Cone Degeneration is a form of PRA known to affect over 40 different breeds.
The retina is a membrane located in the back of the eye that contains two types of photoreceptor cells. These cells take light coming into the eyes and relay it back to the brain as electrical impulses. These impulses are interpreted by the brain to "create" images. In dogs suffering from PRA-prcd, the photoreceptors begin to degenerate, causing an inability to interpret changes in light. This results in a loss of vision. Rod cells, which normally function in low-light or nighttime conditions, begin to degenerate first. This leads to night-blindness. The cone cells, which normally function in bright-light or daytime conditions, will deteriorate next. This often leads to complete blindness over a period of time.
PRA-prcd is inherited as an autosomal recessive disorder. A dog must have two copies of the mutated gene to be affected by PRA. A dog can have one copy of the mutation and not experience any symptoms of the disease. Dogs with one copy of the mutation are known as carriers, meaning that they can pass on the mutation to their offspring. If they breed with another carrier, there is a 25% chance that the offspring can inherit one copy of the mutated gene from each parent, and be affected by the disease.
Progressive Retinal Atrophy (PRA) is a category of genetic mutations that cause vision loss and blindness. Photoreceptor cells in the retina begin to degenerate, typically progressing from a loss of night vision to complete blindness.
PRA affects many different dog breeds, and these mutations are breed-specific. In Golden Retrievers, two mutations have been identified in addition to prcd-PRA known as GR-PRA1 and GR-PRA2.
Both GR-PRA1 and GR-PRA2 are inherited in an autosomal recessive manner. This means that a dog must inherit a copy of the mutation from each parent to be affected by the disorder. Dogs with one copy of the mutation will not show any signs or symptoms of PRA, however, they can still pass on that mutation to any offspring.
Ichthyosis is an autosomal recessive genetic mutation that affects the skin of Golden Retrievers. The mutation prevents the outer layer of the epidermis from forming properly, resulting in skin that becomes darkened and thick, with excessive flaking.
The name "Ichthyosis" is derived from the Greek word for fish. This describes the skin's resemblance to fish scales. The most common symptom of ICH-A is excessive flaking of the skin. Other symptoms include areas of hardened skin and hyperpigmentation, which may make the skin appear dirty or blackened. Symptoms can be mild or severe. Evidence of the disease may be detected when the dog is still a puppy, but symptoms may take a year or more to develop. Additionally, symptoms can improve or worsen, depending on stress and hormonal cycles.
Ichthyosis is generally not dangerous to a dog's health, but can be unsightly and uncomfortable for the dog. ICH-A is frequently related to other health issues such as yeast overgrowth and fungal infections. A dog diagnosed with ICH-A will usually require more care with special shampoos and treatments.
ICH-A is unfortunately quite common in Golden Retrievers, but can be identified with a simple DNA test. A dog with ICH-A would need to inherit the mutation from both parents, as the mutation is autosomal recessive. Asymptomatic carriers and affected dogs can be identified prior to breeding to avoid producing offspring with ICH-A.
Degenerative Myelopathy (DM) is a progressive neurological disorder that affects the spinal cord of dogs. Dogs that have inherited two defective copies can experience a breakdown of the cells responsible for sending and receiving signals from the brain, resulting in neurological symptoms.
The disease often begins with an unsteady gait, and the dog may wobble when they attempt to walk. As the disease progresses, the dog's hind legs will weaken and eventually the dog will be unable to walk at all. Degenerative Myelopathy moves up the body, so if the disease is allowed to progress, the dog will eventually be unable to hold his bladder and will lose normal function in its front legs. Fortunately, there is no direct pain associated with Degenerative Myelopathy.
The onset of Degenerative Myelopathy generally occurs later in life starting at an average age of about 10-12 years. However, some dogs may begin experiencing symptoms much earlier. A percentage of dogs that have inherited two copies of the mutation will not experience symptoms at all. Thus, this disease is NOT completely penetrant, meaning that while a dog with the mutation can develop Degenerative Myelopathy, the disease does not affect every dog that has the genotype.
GRMD is a mutation of the dystrophin gene that causes a deficiency of dystrophin proteins in Golden Retrievers. The lack of dystrophin proteins 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 at about 6 months of age.
The GRMD mutation is sex-linked and located on the X chromosome. So while both male and female dogs can be affected, GRMD is mostly a disease related to male Goldens. Females can be carriers of the mutation, however, will not exhibit any symptoms. DNA testing to identify both male and female carriers is important to remove them from the breeding population.
Chondrodysplasia (CDPA) is a general term used to describe a genetic skeletal trait affecting the development of cartilage growth plates. It is generally characterized by a normal sized trunk and shorter than normal limbs.
Chondrodystrophy (CDDY) refers to abnormal cartilage growth and bone development. Many dog breeds like Dachshunds, Bulldogs, Corgis, Pugs, French Bulldogs, Bassett Hounds, Pekineses, Lhasa Apsos, Shih Tzus, Beagles, etc. are defined as having shorter than normal limbs. Other skeletal characteristics that are sometimes associated with chondrodysplasia in dogs are: a lower jaw that may protrude further than normal, an unusually short upper jaw, or over under bite with crooked teeth. Bowed front legs, a crooked spine or breathing problems are also often found to be a problem. In 2009, a discovery found that dogs with CDPA have an autosomal dominant FGF4 insertion on chromosome 18. This promotes the short-legged phenotype. Fibroblast growth factor-4 (FGF4) is a common protein involved in early development on cartilage and bond length. This growth factor is directly correlated to limb development.
Neuronal Ceroid Lipofuscinosis is a progressive degenerative disease of the central nervous system. In Golden Retrievers, NCL is caused by a two base pair deletion in the CLN5 gene. This causes a frameshift in the genetic coding, leading to a premature termination codon.
Golden Retrievers with NCL begin to develop signs of the disease around 13 months old. Often the first sign of NCL is a loss of coordination during basic movements including walking, running, and climbing stairs. Sings of the disease are particularly noticeable when the dog is excited. As the disease progresses, the loss of coordination becomes evident even when the dogs is calm; the dogs may also experience tremors, seizures, or blindness. Compulsive behaviors, anxiety, and loss of previously learned behavior is also common. Affected dogs may also become agitated or aggressive as the disease continues to progress. Due to the severity of the disease and loss of quality of life, most affected dogs are euthanized by 2-3 years of age.
Because NCL is recessive, a dog must inherit a copy of the mutation from each parent in order to be affected. No signs of NCL will appear if the dog has only one copy of the mutation, although it will be a carrier of the disease. When breeding two carriers together, there is a 25% chance per puppy born that it will develop symptoms of NCL.
Osteogenesis Imperfecta (OI) or Brittle-bone Disease is an inherited autosomal recessive disease. The genetic mutation impairs the normal development of collagen, which causes bones and teeth to be thin and brittle. Although bones are of normal length, they can break or fracture easily due to low bone density. Once an injury occurs, healing can be slow or incomplete.
In addition to brittle teeth and bone fractures, symptoms of OI can also include loose joints, weak muscles and tendons, a curved spine, and hearing loss. In severe cases, dogs with OI will have to be euthanized. There is no cure for OI, but with proper care and caution dogs can still have decent quality of life.
While Osteogenesis Imperfecta is most commonly associated with Dachshunds, the disease has also been detected in Golden Retrievers and Beagles.