Overview and Prevalence of Genetic Defects
in the Rhodesian Ridgeback

By Cynthia Roethel, Senior Chair
RRCUS Health and Genetics Committee

 In 1996, the Rhodesian Ridgeback Club of the United States undertook the task of coordinating a nationwide health survey for the breed. The purpose of that survey was – and still is – to develop a better understanding of the health issues affecting Ridgebacks.

Since the survey’s inception a decade ago, there have been two tabulations of the data: the first after the initial data collection in 1996 and another in 2001. The information the health survey gives us is an invaluable tool: Besides identifying health issues, it allows us to monitor changes that might indicate an increase or decrease in the occurrence of a particular disease. 

At the 2002 Rhodesian Ridgeback Specialty in Lansing, Mich., the late canine geneticist and veterinarian Dr. George Padgett, DVM, presented a seminar on the “Control of Canine Genetic Disease.” Dr. Padgett was given our health survey to analyze, and he tailored his presentation to Rhodesian Ridgebacks. Going through our health survey, Dr. Padgett highlighted those diseases and conditions known to be heritable (genetic). His criteria for including a genetic disease were very straightforward: There had to have been an occurrence in at least one member of the breed that was confirmed by a qualified veterinary diagnostician.

Dr. Padgett acknowledged that there is a chance of error, but he asked us to consider that the best time to stop a genetic disease is when there is only one or perhaps a few cases of it in the breed. He reminded us that if 1 percent of the population is affected with a genetic disease whose mode of inheritance is recessive, it means that 18 percent of the population are carriers.

Dr. Padgett and I discussed where the Rhodesian Ridgeback stands in terms of genetic disease, and he commented that the breed is in the lower middle range in terms of number of genetic defects in purebred dogs.  Dr. Padgett also confirmed a hunch I have had for a long time: That clubs that actively pursue getting a handle on the health of their breed by doing comprehensive health surveys will always have a higher number of genetic defects identified, and that number will always be higher than what was previously assumed. (For more information about purebred dog breeds and genetic defects consult Dr. Padgett’s book, “Control of Canine Genetic Disease.”)

The Rhodesian Ridgeback health survey was designed to monitor trends over time. If all Ridgeback owners provide surveys on all Rhodesian Ridgebacks born after January 1, 1984 (healthy or not), and updated them when necessary, a diagnostic error would very quickly become obvious, as the disease frequency would decrease to nearly nothing. The need for health surveys on all Ridgebacks cannot be over-emphasized. This includes healthy, unaffected dogs, as well as dogs with health problems.

The health survey is a tool for us to critically evaluate the health of the Rhodesian Ridgeback breed as a whole. No survey is perfect – there can be numerous errors in the reporting of disease, starting at the veterinarian’s office and ending at the table when you fill out the survey. NONETHELESS, this is the best tool we have to assess the health of our breed.

In 2006, the RRCUS Health and Genetics Committee will debut a new electronic health survey that will be far easier to use than its paper-only predecessor, and which assures total confidentiality. Whether this survey is truly reflective of the health of our breed is solely dependent on YOU. See the Health Survey page for more information and instructions.

The diseases, modes of inheritance, frequency of each disease and Dr. Padgett’s guesstimation for gene frequency in the Rhodesian Ridgeback are listed below. These are in the order in which they appear in the health survey and are in no way prioritized. Also, the severity of the diseases varies widely. Some have little to no impact on the life of the dog with treatment, while others are severely debilitating.

Based on the data in the health survey, Dr. Padgett determined that each Rhodesian Ridgeback carries genes for approximately 6.6 of these genetic defects, which is about the same as we carry as humans. Dr. Padgett asserted that knowing which 6.6 genetic defects your Ridgeback carries, prioritizing them and then breeding away from them is the key to controlling canine disease.

GENETIC DISEASE, DISEASE FREQUENCY AND GENE FREQUENCY IN THE RHODESIAN RIDGEBACK

	Age at diagnosis	Disease	Mode of inheritance	Disease frequency	Guesstimation of gene frequency (%carriers)
1	<8 years	Hypothyroidism	R	5.0/100	34.7%
2	<5 years	Addison's disease	UND	0.2/100	8.4%
3	<8 years	Hyperadrenocorticism	UND	0.1/100	6.0%
4	<3 years	Diabetes mellitus	UND	0.06/100	4.7%
5	<4 years	Hyperparathyroidism	UND	0.06/100	4.7%
6	<4 years	Autoimmune hemolytic anemia	UND	0.1/100	6.0%
7	<6 years	Immune mediated polyarthritis	UND	0.06/100	4.7%
8	<10 years	Immune mediated thrombocytopenia	UND	0.06/100	4.7%
9	<9 years	Systemic lupus erythematosus	UND	0.06/100	4.7%
10	<1 year	Von Willebrand's disease	R, Dinc	0.06/100	4.7%
11	birth	Hemophilia	X-R	0.06/100	4.7%
12	>4 years	Mast cell tumor	POLY	3.5/100	30.5%
13	>4 years	Hemangiosarcoma	POLY	0.6/100	14.2%
14	Birth	Ridgelessness	Complex	10.6/100	43.9%
15	<3 months	Dermoid sinus	R	4.7/100	33.9%
16	<1 year	Demodicosis	UND	1.5/100	21.4%
17	<1 year	Atopic dermatitis	UND	3.6/100	30.6%
18	<1 year	Food allergies	UND	1.2/100	19.4%
19	<5 years	Seasonal flank alopecia	UND	0.1/100	6.0%
20	<10 weeks	Ehlers Danlos syndrome	D	0.06/100	4.7%
21	<10 weeks	Umbilical hernia	R/Poly	0.5/100	13.1%
22	<6 months	Megaesophagus	R/UND	0.9/100	17.0%
23	<7 years	Pancreatic hypoplasia	R	0.06/100	4.7%
24	<1 year	Gastric Dilatation/Volvulus	UND	0.9/100	17.0%
25	<1 year	Subaortic stenosis	POLY	0.2/100	8.4%
26	< 2 years	Cardiomyopathy	POLY	0.1/100	6.0%
27	Birth	Persistent right aortic arch	POLY	0.06/100	4.7%
28	<1 year	Pulmonary stenosis	POLY	0.06/100	4.7%
29	<1 year	Laryngeal paralysis	D	0.06/100	4.7%
30	<1 year	Tracheal collapse	UND	0.1/100	6.0%
31	<3 months	Cryptorchidism	R/UND	1.0/100	18.0%
32	>1 year	Seizures (epilepsy)	R/UND	0.7/100	15.2%
33	>1 year	Degenerative myelopathy	UND	0.5/100	13.1%
34	<6 months	Deafness	UND	0.3/100	10.2%
35	</= 1 year	Wobbler syndrome	POLY	0.1/100	6.0%
36	<9 years	Cauda equina syndrome	UND	0.06/100	4.7%
37	<3 months	Hydrocephalus	POLY	0.06/100	4.7%
38	<1 year	Lumbar stenosis	UND	0.06/100	4.7%
39	<2 years	Hip dysplasia	POLY	2.20/100	25.2%
40	<1 year	Dental abnormalities	UND	1.40/100	20.8%
41	<1 year	OCD/FCP (elbow dysplasia)	POLY	0.7/100	15.2%
42	<1 year	Luxating patella	R	0.10/100	6.0%
43	<1 year	Osteochondritis dissecans	UND	0.4/100	11.7%
44	<1 year	Congenital vertebral abnormalities	UND	0.3/100	10.2%
45	<3 months	Open fontanelle	UND	0.2/100	8.4%
46	>1 year	Spondylosis deformans	POLY	0.2/100	8.4%
47	<4 months	Pectus excavatum	UND	0.1/100	6.0%
48	Birth	Cleft palate	POLY/UND	0.1/100	6.0%
49	<8 months	Hypertrophic osteodystrophy	UND	0.1/100	6.0%
50	varies	Cataracts	UND	1.0/100	18.0%
51	<6 months	Entropion	UND	0.6/100	14.2%
52	<3 months	Persistent pupillary membranes	UND	0.2/100	8.4%
53	<3 years	Glaucoma	UND	0.1/100	6.0%
54	<6 months	Ectropion	UND	0.6/100	4.7%
55	varies	Corneal dystrophy	UND	0.6/100	4.7%
56	Birth	Microphthalmia	UND	0.6/100	4.7%
57	<= 3 years	Excessive aggression	UND	1.8/100	23.2%
58	<1 year	Excessive Shyness	UND	0.8/100	16.2%