Inherited conditions in the Rhodesian Ridgeback - A Breeders perspective by Vicki Moritz

Introduction:

The Rhodesian Ridgeback is a relatively recent breed, first recognised and registered in 1924 by the South African Kennel Club. The recent formation of this breed has provided some genetic vigour, but also diversity in the “type” or “style” of the Ridgeback. In relative terms and in the generalist press the Ridgeback appears to have few genetic issues, and compared with many other pure breed dogs this may be the case. However there is no room for complacency. George Padgett in “Control of Canine Genetic Diseases” listed 26 diseases of genetic origin reported in the Ridgeback¹. In a 2002 seminar at the US Ridgeback specialty a further list containing 58 genetic conditions was developed.  His research showed that any one dog will carry a number of genes that are defective and may cause inherited conditions. His analysis of the Ridgeback determined each Ridgeback carried genes for approximately 6.6 issues.^2,3 Experienced breeders know the breed is subject to a considerable number of inherited conditions, many cosmetic, which make the breeding of Ridgebacks suitable for the conformation ring a challenge. This is certainly borne out by Padgett’s analysis and the figures below. These demonstrate that over 27% of pups born are unsuitable for show or breeding due to ridge issues alone.

Selection of the best breeding stock in Ridgebacks- and pedigree dogs in general- is always a challenge no matter how much research is done on the pedigrees and characteristics of both parents. In addition to the obvious phenotypic factors such as structure, movement etc, inherited diseases must be taken into account.  In many cases the inherited conditions are polygenic, that is controlled by a number of genes and expressed variably. This makes elimination of affected animals from the gene pool complex, as they may be carriers who never produce a defect they may be carrying. It is a responsibility of the breeder to weigh up the importance of any genetic defects the animal may be carrying and balance it with the overall quality of the animal. There is no place for kennel blindness in this assessment!

Data on genetic conditions affecting Ridgebacks in Australia was gathered in 1996 and again in 2006. The latter survey was done under the auspices of the National Rhodesian Ridgeback Club with 25 breeders providing information on 1397 dogs.  In the USA the Rhodesian Ridgeback Club of the US (RRCUS) conducted Health Surveys in 1996 and then again in 20002. 1763 dogs were represented in their 2000 survey. Selected comparative survey results are as follows, with the US data sourced from the 2002 “Overview of genetic issues” paper by Cynthia Roethel³

*1   May be under reported in Australia, as accurate reporting assumes follow up and/or testing. Many US breeders screen for a range of genetic conditions including autoimmune thyroid conditions and heart issues prior to breeding. The analysis of the 2006 Australian data stated the following “When considering the information provided, it must be accepted that conditions not seen prior to the pup leaving the breeder are likely to be under reported in this survey. These include heart murmurs, entropion, torsion/bloat, neurological problems, hip dysplasia, hypothyroidism, skin problems/allergies, cancers (including mast cell), elbow disease, and other skeletal issues.”

Inherited conditions fall into two main categories- those which require intervention and those that are mainly cosmetic, which generally mean the affected animals are sold as pets and de-sexed.

Inherited conditions requiring veterinary attention

Dermoid sinus

This is the inherited condition most commonly thought of in association with Ridgebacks. It is related to the formation of the ridge and similar to spina bifida in humans. It is generally detected at birth (by most breeders and some veterinary surgeons), and in this country most affected animals are euthanised (although in the US by 2000 only 52% were euthanised)². The dermoid sinus is felt as a fine thread from the skin surface going down toward the vertebrae- and keep in mind some animals may have multiple sinuses. It is generally felt along the midline between the occiput bone and the beginning of the ridge, or from the end of the ridge and down into the tail. However, sinuses have been reported by some breeders as tracking through the epithelial surface and surfacing elsewhere such as on the cheek area. Left unchecked, epithelial cells may slough off into the sinus and cause the area to abscess.

An early paper on Dermoid sinus suggests inheritance is dominant with “inconstant penetration”4. A study has recently been published which determined the allele responsible for the ridge and demonstrated a link between dermoid sinus and the ridge5.  They noted that in selectively breeding dogs with ridges together and removing ridgeless dogs from the breeding population, the genetic sequence that codes for both the ridge and dermoid sinus is over represented! Their findings are not surprising as my experience is such that where there are more ridgeless pups born (Rr parents), there is less dermoid sinus.

Hip Dysplasia

Most Ridgebacks in Australia and other countries are now X-rayed for hip dysplasia prior to breeding. Selective breeding in the US has reduced the incidence from 11.8% dysplastic dogs born prior to 1980 to 3.4% for dogs born in 2003/2004⁶. Two main schemes are used in Australia for grading of hips- the British Veterinary Association (BVA) scheme, and more recently the PennHip scheme, with the BVA scheme being the most common. There are a number of views and articles on the relative value of each scheme⁷. In 2008 the BVA overall breed mean score for Ridgebacks is 11⁸. The breed average in Australia is approx ^6.7.

It is an uncommon but debilitating condition. In my experience some Ridgebacks are radiologically but not clinically dysplastic. However, the ideal is to chose breeding stock from those dogs with scores less than or around the breed mean score, while still keeping in mind the need to weigh up the quality of the whole animal when selecting breeding stock eg don’t throw away the baby with the bath water!

Gastric Dilation and Bloat

This is a life threatening condition, characteristic of large deep chested dogs and is sometimes seen in the Ridgeback. Early signs of this condition include attempts to vomit, restlessness, hunched up appearance and then a swelling abdomen⁹. One of the most comprehensive studies on this condition was undertaken by the Purdue University in the US and they concluded risks increased with:

• Increasing age
• Increased thorax depth/width ratio (eg more depth, less width)
• Having a first degree relative with a history of Bloat
• A faster speed of eating
• Using a raised food bowl¹⁰

Other studies have also implicated stomach tumours, a narrowed pylorus, eating non digestible foodstuff, stress and fear, eating only one meal a day, nasal mites (which contribute to air swallowing) and anything that delays gastric emptying^9,11.

Elbow and Shoulder disease 

The term “Elbow disease” covers a number of conditions such as ununited anconeal process (UAP), fragmented medial coronoid process (FCP) and osteochondrosis (OCD)¹². Breeding stock are increasingly Xrayed for elbow dysplasia, although the low incidence of problems in this area have made this a recent phenomenon. Willis¹³ states that while there is breed predisposition for OCD, genetic overtones are uncertain. Recent work suggests elbow disease is inherited and animals with any evidence of elbow dysplasia (score of 1 or above) are breeding risks. This is a change in thinking from earlier days where dogs with scores 2 and above were regarded as breeding risks¹⁴. OFA figures from 2007 put elbow dysplasia in US Rhodesian Ridgebacks at 6.5%¹⁵.

Shoulder disease is more rarely reported, but OCD of the shoulder has been reported in the breed.

Eye problems:

Entropion (in-growing eyelids) is sometimes seen in the Ridgeback, and if early surgical correction is undertaken, rarely causes an on going problem. However, this is an inherited condition and affected animals should not be bred from. Cataracts, persistent papillary membranes, ectropion, corneal dystrophy and glaucoma have also been reported as inherited issues³.

Heart “murmurs”:

This term covers a number of clinical conditions. Cardiac conditions may be diagnosed by vets following detection of “heart murmurs”, which are caused by a variety of different cardiac problems. More specific diagnosis may need expensive diagnostic procedures to determine the cause and severity of the condition. The most common heart defects resulting in murmurs are patent ductus arteriosus (PDA-also seen in humans) and subaortic stenosis (SAS).

Other heart defects with an inherited basis seen in the breed include cardiomyopathy, persistent right aortic arch and pulmonary stenosis³. Some conditions can be detected by routine screening of pups prior to sale, but others such as SAS may not be found until later in life. It is not recommended to breed from animals with these conditions. It is also interesting to note that heart conditions are one of the few areas where numbers have increased between 1996 and 2006, and where the Australian numbers are higher than the US.

Thyroid problems and autoimmune disease:

Hypothyroidism is thought to be an inherited condition in the Ridgeback, and the US figures demonstrate a high prevalence in that country³. Comparative figures from other countries would be of interest, but few countries undertake this test as a routine screening procedure as yet! It can be hard to diagnose but signs may include incessant whining, nervousness, hyperactivity, failure to be attentive and unprovoked aggression¹⁶.

Hypothyroidism is generally a result of autoimmune disease which destroys the thyroid gland¹⁶. Other autoimmune diseases which have been reported in the breed include Addison’s disease, hyperadrenocorticism, autoimmune haemolytic anaemia, systemic lupus erythematosus (SLE) and degenerative myelopathy³. Autoimmune diseases are thought to have an inherited component, but some may not manifest without environmental triggers¹⁷

Hernias:

These have been reported in the breed, generally seen as umbilical hernias. Depending on severity they may need surgical correction. It is suggested the condition is inherited as a polygenetic theshold character¹³.

“Wobblers syndrome” (Spondololithesis):

This is sometimes seen in the rapidly growing young dog, and is seen in the Ridgeback. It is characterized by increasing “clumsiness” and loss of rear leg co-ordination and may result in paralysis¹. Recent veterinary progress has offered new techniques for treatment of this condition.¹⁸ A genetic basis has been reported, and such animals should not be bred from¹³.

“Swimmers” (Pectus excavatum):

This condition is rarely seen and characterised by new born pups which seem “flattened” and incapable of standing. It appears to be inherited and culling is recommended.¹³

Monorchidism:

In some cases the one (or more rarely, both) testicles do not descend in the male pup. Breeders should check male pups carefully prior to sale as potential breeding animals, and ensure the desexing of dogs with one or no testicles. This is important as the retained testicle(s) may become malignant.

Chronic skin conditions:

Some Ridgebacks are prone to allergic dermatitis and some skin conditions have an inherited basis due to autoimmune disease^1,13. Allergic dermatitis can be distressing for dog and owners, and in some lines it may be necessary to select against this condition.¹⁹ Systemic diseases such as hypothyroidism and Cushing’s Syndrome (hyperadrenalcorticism) can also manifest as skin conditions.²⁰

Oncological Diseases (Cancer):

As with most animals (including humans), Ridgebacks are prone to cancer. I have lost older Ridgebacks with Osteosarcoma and Malignant Melanoma. The US figures suggest Mast Cell Tumours are prevalent in the breed and they have been reported in Australian Ridgebacks. Mast Cell Tumours are thought to have a genetic component, with some suggestion this also be the case for Osteosarcoma.^21,3

Cosmetic inherited issues:

This is where we leave the realm of science and enter a more subjective arena.

The Ridge:

While this is the “escutcheon” of the breed, breeders have to contend with ridgeless pups, short ridges, animals born with offset (not parallel) crowns, or less or greater than two crowns. Many otherwise fine animals are sold as pets as their ridges are not suitable for the conformation ring. Breeders, and indeed judges, will vary in what degree of “offset” they will accept for the crowns, but should agree that animals with more (or less) than two crowns should not be bred from.

Structure:

As with any breed many structural faults appear to “run in families”. These may include poor fronts (lacking, or too wide), short muzzles, bad mouths, muzzles lacking in depth, “cheeky” heads, heads lacking in stop, high set ears, poor toplines, poor feet, steep croups or those lacking in slope resulting in high set tails etc etc. Also, as with other breeds, in many cases the worst of the structural defects are those which result in poor movement, with lesser defects more cosmetic in nature. Kinked tails, short and overlong tails are sometimes seen, and little has been done to look at the inheritance of these characteristics- although it is suggested kinked tails are inherited.

In my experience dental problems are associated with head structure eg lines with less depth of muzzle may see more overshot jaws, those with shorter and deeper muzzles are more likely to have issues with undershot jaws.

Coat Colour:

The breed standard calls for a light wheaten to red wheaten coat, with breeders sometimes debating what is too light or too dark. The standard of 1922 also allowed for brindles, sables “or mixed with white”, and excess white and black is sometimes still seen. Most breeders tend to judge these animals on their merits and an otherwise outstanding specimen with a long white sock or excess black will be bred with by some breeders, but perhaps not by others. Blue/Greys (either a Weimeraner type grey, or a blue/grey overlay on a red coat) and black and tan colourings are rarely seen in litters, and should not make the show ring or be bred from! The genetic recessive “brown nose” with a flesh coloured nose and light eye is quite acceptable in the breed and should be judged on conformation like any other Ridgeback.

Additional whorls in the coat:

In my experience these are not unusual and may be seen on the hindquarters, each side of the tail or on the neck below the ears. In some litters pups may also be born with whorls or crowns on the occiput area. They are also more rarely seen on the shoulders. Additional whorls on the top of the head or shoulders are usually penalised by breeders, whereas those on the hindquarter or sides of the neck are less likely to be seen as unacceptable.

Breeders responsibilities:

In cases of inherited conditions requiring veterinary intervention or severely affecting the health of the animal, the response of the breeder to finding an inherited condition should be clear cut. Do not breed from the affected animal and risk transmitting the condition to future generations. In the current age of litigation breeders should also be aware that knowingly breeding from faulty stock may result in puppy buyers successfully suing the breeder.

However, there are cases where the decision to breed from an animal is not so clear cut eg should an excellent specimen of the breed with a slight tail kink, too much black or white, or a crown on the head be removed from the breeding pool? I’m not proposing to answer this question, but only to remind breeders that they are the custodians of their breed, and must breed with care and knowledge of the genetic make up of their animals. It must be remembered that all our animals carry some genetic issues, so careful breeding must be done to minimise doubling up on any problems. Genetic information can only be obtained through the honesty of breeders with each other, and by screening of animals for breed related genetic defects prior to breeding.

The question of how much screening should be done is yet to be resolved. The following is taken from the Code of Ethics for members of the RR Club of the USA:

"Only dogs screened and certified clear of hip and elbow dysplasia by the Orthopedic Foundation for Animals, Pennhip or comparable foreign registry shall be bred. Other recommended genetic testing includes a complete thyroid panel* from an OFA-approved laboratory or canine endocrinologist, cardiac certification (OFA or cardiologist evaluation) CERF*(Canine Eye Registration Foundation) and BAER (Brainstem Auditory Evoked Response or hearing test). Breeders shall endeavor to stay current in their knowledge of all known inheritable diseases present in the breed and demonstrate reasonable care in eliminating those diseases (*indicates annual re-test requirement)”.

At present most Australian breeders are required by breed clubs to screen for hip and elbow dysplasia. If not in a breed club, there are no breeding requirements. Perhaps it is time to reconsider the level of testing undertaken to maintain the health of our breed, and to better inform our breeding selections? It is certainly time to be honest with each other for the betterment of our breed.

Vicki Moritz
Ujamaa Ridgebacks
July 2008

     References:

1. Padgett, GA, 1998 Control of Canine Genetic Diseases. Howell Book House, NY
2. Rhodesian Ridgeback Club of the United States, Inc. 1996 National Health Survey Update April 2001 http://www.rhodesianridgebackhealth.org/index2.shtml
3. Roethal, C 2002 Overview and Prevalence of Genetic Defects in the Rhodesian Ridgeback 
   http://www.rhodesianridgebackhealth.org/resources/overviewgeneticdesease.html
4. Mann, GE and J Stratton 1966 Dermoid Sinus in the Rhodesian Ridgeback J Small Anim. Pract. Vol 7 1966 pp631-642
5. Hillbertz, Nicolette HCS, Magnus Isaksson, Elinor K Karlsson, Eva Hellme, Gerli Rosengren Pielberg, Peter Savolainen, Claire M Wade, Henrik von Euler, Ulla Gustafson, A° ke Hedhammar, Mats Nilsson, Kerstin Lindblad-Toh, Leif Andersson and Goran Andersson. 2007 Duplication of FGF3, FGF4, FGF19 and ORAOV1 causes hair ridge and predisposition to dermoid sinus in Ridgeback dogs. Nature Genetics 39(11): 1318- 1320
6. Hip Dysplasia Statistics. Trends in Hip Dysplasia. 2008. Orthopedic Foundation for Animals, 2002 http://dogphenome.org/hipstatbreed.html?view=2
7. Moc Klinkam Canine Hip and Elbow Dysplasia Resources Rev. June 3, 2002
8. http://www.workingdogs.com/doc0090.htm
9. British Veterinary Association/Kennel Club Hip Dysplasia Scheme- Breed Mean Scores at 01/11/2007
10. Landers, P What’s new about Bloat. 2001 http://www.mirage-samoyeds.com/bloat-lecture.htm
11. Glickman, LT, Glickman, NW, Schellenberg, DB, Raghavan, M, Lee, T.Canine 2000 Gastric Dilatation-Volvulus (Bloat) School of Veterinary Medicine Purdue University, West Lafayette, US Non-dietary risk factors for gastric dilatation-volvulus in large and giant breed dogshttp://www.vet.purdue.edu/epi/update2.htm
12. Arndt, L. Nutrition: Is it a factor in Bloat and Torsion. http://devinefarm.net/rp/rpfbloat.htm
13. Elbow disease in growing dogs. 2001 Extracted from a paper from Dr Roger Lavelle. http://rhodesian-ridgeback.nu/page/hdad.html
14. OFA Questions and Concerns Regarding Elbow Dysplasia  http://www.offa.org/edanswers.html
15. Willis, BM 1989 Genetics of the Dog. Witherby Ltd
16. Elbow Dysplasia Statistics 2008 Orthopedic Foundation for Animals. http://www.offa.org/elbowstatbreed.html
17. Canine hypothyroidism, J Dodds http://www.workingshelties.org/HypothyroidismSimplified.htm
18. Canine Autoimmune Disease. J Sampson. 2006 http://www.englishspringer.org/downloads/Auto%20Immune%20Disease%20-%20Jeff%20Sampson%20ESSC%20Website%20Insert.pdf
19. Lyman, R 2003. Know signs, therapeutic options for canine Wobbler syndrome http://veterinarynews.dvm360.com/dvm/article/articleDetail.jsp?id=48328
20. Shaw, S Atopic Dermatitis in the Dog. http://priory.com/vet/vetatop1.htm
21. Dog Skin Disorders 2008 http://en.wikipedia.org/wiki/Dog_skin_disorders
22. Osteosarcoma 2008 http://en.wikipedia.org/wiki/Osteosarcoma