DNA Testing

DNA Testing

DNA tests are available for Rhodesian Ridgebacks through Orivet ( Orivet Rhodesian Ridgeback Products ) or Massey University DNA via Dogs Qld Web site (Massey University DNA)

Sajanak Ridgebacks obtain the Rhodesian Ridgeback Full Breed Profile testing for several items for genetic diseases, conditions, and traits. Genetics’ is all about the chance of producing a puppy with or without a given disease, condition, or trait.

When looking at DNA testing, it is only trying to increase the chance that a puppy may or may not have that disease or trait. If a dog is a 'Carrier', then it can live a perfectly healthy life, but it may or may not produce a puppy with that disease or trait. DNA testing is something that breeders can do to increase the chances of avoiding diseases and undesired conditions in their puppies.

There are three main categories in DNA testing - testing for a disease, testing associated with the skin, and testing for a trait.

Genetic Diseases

Degenerative Myelopathy

Signs are due to the immune-mediated destruction of a part of the nerves in the spinal cord, leading to loss of these nerve fibres. The first sign is knuckling of the hind feet, and hind limb ataxia. Once the spinal cord damage progresses past this initial stage (termed proprioceptive deficits), the effectiveness (if any) of treatment is much diminished. Hence early diagnosis is vital. Following this initial stage, hind limb reflexes are affected, then weakness in the hind limbs develops, progressing to total paralysis. Once a dog shows these signs it will almost always respond poorly to therapy. Eventually destruction progresses from the middle of the spinal cord to the upper cord and brain stem, leading to forelimb weakness and eventually interference with the muscles of breathing, causing death. Most dogs are euthanased for humane reasons before this happens. Treatment is with specific supplements and drugs aimed at interfering with the immune destruction in the spinal cord, to slow further nerve damage. The effectiveness of this treatment is variable, but is only of benefit if started as early as possible. Once nerves are lost, they will not be replaced. Degenerative myelopathy cannot be cured. A DNA test is available for predisposed pure breeds to carry out screening of breeding animals.

Generalised Myoclonic Epilepsy (Rhodesian Ridgeback Type)

Also referred to as Junevile Myoclonic Epilepsy (JME). Affected dogs displayed frequent myoclonic jerks or twitches, which start to occur around 6 months of age. Owners of the affected dogs described the myoclonic jerks as severe startling or even resembling an electric shock. The myoclonic seizures can be triggered by visual stimuli, such as light flashes, a sudden incidence of light or flashing light on the sea waves. Photosensitivity was recognized in 35% of dogs. The twiches mostly occur when the dog is in the relaxed state, drowsy or when falling asleep or napping. Twitches can occur also during sitting, standing or walking. There were no noticed changes in the behavior. The myoclonic jerks were mostly limited to the trunk, proximal limb musculature, cervical musculature producing nodding movements of the head, and the face. The intensity can vary between events and affected dogs. After the seizure, the dogs seem confused and scared. Due to the seizures, sleep among those dogs was impaired. The frequency of the twitches can go up to 150 twitches per day.

Dermoid Sinus

The Dermoid Cysts appear on the back in front of and behind the "Ridge" (hairline with opposite growth). They develop embryonic from an imperfect or incomplete separation of skin and spinal cord. If the connection to the spinal canal and spinal cord remains, this can lead to hindquarters paralysis and hyperesthesia (hypersensitivity), infections also cause changes (meningitis, myelitis).

With the Dermoid Sinus (Ridge Gene Test):

Dominant inheritance means that if a puppy inherited ridge gene just from one parent, ridge is present on the puppy´s back. Dog with one ridge gene is called heterozygote (R/r). If a dog inherited ridge gene from both parents, then it is called dominant homozygote (R/R). However, in the litter there may be ridgeless puppies (r/r). Ridgeless puppies are born to two heterozygotes (male and female dog with only one ridge gene). Statistically, in a litter of two heterozygotes there will be born 25% ridgeless puppies .

It has been found that those with dominant RR gene have increased chance of producing Puppies with Dermoid Sinus, where as those with Hetrozygotes (R/r) have normal chance of producing Puppies with Dermoid Sinus, and Ridgeless (r/r) have very low chance of producing puppies with Dermoid Sinus.

When breeding:

  • R/R x R/R have a much higher chance of producing puppies with Dermoid Sinus
  • R/R x R/r have normal chance of producing puppies with Dermoid Sinus
  • R/r x R/r have normal/low chance of producing puppies with Dermoid Sinus
  • A cross with r/r (ridgeless) will almost never produce puppies with Dermoid Sinus

Dermatologic - Associated with the skin

Coat Colour Dilution Alopecia

Colour dilution alopecia is a type of follicular dysplasia, and only occurs when colour dilution is present. A blue coloured animal is the colour dilute form of the normal black and tan colouration, and fawn is the colour dilute form of the normal red colouration. It is thought that there is a defect in the regulation of melanisation (pigmentation) and the structure of the hair cortex, although the underlying genetic defect is not fully understood. Affected animals are born with normal hair coats, but usually signs will be seen between 6 months and 2 years of age, when the hair will begin to break, and patchy alopecia (hair loss) occurs. This usually starts on the back and will progress to widespread hair loss wherever there is light coloured hair. The skin becomes dry and scaly and is prone to infections. Hair that is lost will not grow back. Affected dogs are also susceptible to sunburn and cold

Black Hair Follicular Dysplasia

Black hair follicular dysplasia (BHFD) is inherited as an autosomal recessive trait and is a type of alopecia (hair loss) that only affects areas of black fur. It is seen in bicolour and tricolour dogs. Pups are born normally, but may show a dulling of the normal dark, glossy black hair. The hair on adjacent white skin grows normally. With time black hairs become brittle and break easily. Black hair fails to grow, and skin can become scaly. These abnormal hair follicles are prone to infection, and so affected areas of skin can develop bacterial folliculitis, an infection that is very irritating and can sometimes lead to deeper skin infection (pyoderma).

Traits

It is a trait and so is tested based on preference for the puppy, not usually for health concerns.

A Locus (Fawn/Sable;Tri/Tan Points)

In dogs that do not carry the dominant black gene (ky/ky at the K Locus) and are not "e/e" for the E Locus, the A Locus is allowed to express and determines the colour of the dog's coat. The four alleles work as a hierarchy, with the most dominant allele that the dog has always being expressed (assuming n/n for the K Locus). The most dominant allele is "ay", followed by "aw", then "at", then "a."

Brown Coat Colour Profile (Liver Nose)

This gene is referred to as the B locus and is responsible for brown versus black coat colour with brown coat colour inherited recessive to black. The three alleles of the Brown (B) locus are designated bs, bd and bc, a combination of any two of which will cause brown coat colour. This B locus is the trait for Brown or Liver Nose (bb), with only the recessive (bb) showing the Trait. A dog can be a carrier (Bb) without showing the Trait of Liver/Brown Nose, however they can have Liver/Brown Nose puppies if crossed with another carrier or actual Liver/Brown Nose dog.

D (Dilute) Locus

The protein melanophilin is responsible for the dilute coat colour. This variation causes black, brown and yellow hair (eumelanin or phaeomelanin pigments) to be diluted. Referred to as blue, charcoal, grey and in combination with other colours - lilac or champagne. A normal result is usually reported as DD (no copies of dilute), a carrier as Dd (one copy of the dilute) and a dilute colour dog affected is reported dd.

E Locus - (Cream/Red/Yellow)

DNA variant in the MC1R gene (e) shuts down production of eumelanin (black pigment) in the melanocytes leaving only the production of phaeomelanin (yellow/red pigment) in the melanocytes. Because e is recessive, two copies of this e variant must be present to express the solid “yellow/red” coat color. A dog that has two copies of E (E/E) will not have a yellow/red coat and will not be capable of passing on a yellow/red coat color Allele to its offspring.

DNA Profile

Canine DNA Profile (ISAG Canine 288 SNP Panel) Parentage Verification is to confirm with DNA if the advertised parents are the real parents of the litter