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By Diane Jacobsen
4561 Todd Road
Sebastapol, CA 95472-5227
dijs@aol.com

(These two articles are also located on the RRCUS site at www.rrcus.org)

The dermoid sinus (D.S.) has been known by many names, a few of which are dermoid cyst, hair cyst, and African cyst. It is a sinus, in that it is tubelike and does drain, and dermoid because it is skinlike. It may or may not contain hair follicles or be lined with hair. As the hair sheds on the outer coat of the pup, so does the hair inside this tube. The body’s natural response to dead material is to flush it out and thus the serum builds up and expels the debris., Not all of the dermoid sinuses are true tubes. Some are not hollow and the serum and debris cannot drain. In these cases an abscess forms and the resulting swelling that accompanies can rupture the skin. This results in a very painful situation for the pup. At its worst it is life threatening.

The D.S. is generally found on the midline of the neck, back, and tail along the spinal column. Although rarely found in the ridge there have been several cases noted. Dermoid sinuses have also been noted on ridgeless puppies.

The D.S. is a congenital condition, meaning that it is present at birth. It can be palpated on the newborn pups, and the affected pups identified. The affected pups should be put to sleep or if they are to be kept, surgery to remove the D.S. should be performed before sending them to their new homes. The affected pups are pet stock only and should not be considered as breeding material.

To find the D.S. you must palpate along the midline of the spine, starting at the top of the head close to the occiput (bump) bone. To do this you may pick the pup up and hold it in the cup of your hand or palpate as the pup is sleeping. Take the other hand and envision yourself picking up a baby kitten by the scruff of the neck with your thumb and forefinger. Exert enough pressure to feel, but not enough to bruise. Use your whole hand as one unit, pulling first up toward the nose and then down toward the tail. The skin will stretch quite a bit in both directions. Do not roll the skin through your fingers. The fingers remain exactly where you placed them on the skin. The D.S., being attached on the top to the skin and at the base to the spinal cartilage, will slip through your fingers. A large D.S. will feel like a wet noodle and a finer D.S., like a small string. Reposition your fingers on the neck just below the starting spot and repeat this process. Continue to work your way down the neck and back to the tail.

At the tail it is very difficult to raise enough skin to palpate effectively. It is best to use your thumb in this area. With fingers underneath the pup supporting it, place the flat of your thumb over the spinal column at the pelvic area. Push skin first to one side and then back to the other side. Again, remember that the D.S. is attached and will slip under your thumb. This will feel like a squiggly noodle on a larger, longer D.S., or just an area that simply will not move at all on a shorter D.S. If you do not feel anything by sliding the skin from side to side, try sliding the skin toward the nose and then back to the tail, taking care to slide the skin, not your thumb.

As you palpate the area over the shoulders, you may feel connective tissue that holds the skin to the shoulder area. The tissue is heavier in this area than in the other areas of the spinal column. It will feel flat and you will not be able to trace it from the area close to the muscle all the way to the skin, whereas the D.S. is easily traced from the muscle to the top of the skin and feels round.

The D.S. can be visually detected by looking for a group of hairs that protrude straight up out of the hair coat of the pup. When you see this, the pup should be palpated for a D.S. The hair can also be shaved at this site and upon examination, a small dimple will be revealed. By moving the skin back and forth, the dimple will become more apparent as the anchor of the D.S. will pull the skin down more.

The D.S. can be surgically removed. It is advised that a vet be contacted that is familiar with this condition and has performed this operation before. Dermoid sinuses are not alike in their makeup and it is impossible to tell which ones are easily removed or which ones go to the spine. They can wrap around or enter the area of the spinal cord, which makes them almost, if not impossible, to remove. In cases such as this some success has been achieved by folding the D.S. over and tying it off, but some have had regrowth. Since there is no way to detect which type of D.S. that the pup has, instructions to the vet should include that if the D.S. is not completely removable, the pup be put to sleep. D.S. pups should not be promised to a new home until after the surgery.

The healing process can be as traumatic as the operation itself. In the simple cases that remove easily, there will be little or no serum build-up in the surgical area. In the more complicated surgeries, where the tissue damage has been more severe, the serum will start building up as soon as the surgical site heals over on the top of the skin. Usually this will be on the fourth or fifth day. This requires aspiration with a large guage needle and syringe, sometimes three or four times daily, to remove the serum build-up. This can last for three to 10 days after surgery.

Pups that have had surgery must be removed from the litter to prevent damage to the surgical site. As puppies play, they grab and shake areas of skin on the other pups. If they were to grab and shake over or near the surgical site, damage would occur and the serum buildup would become a bigger problem.

Dermoid sinuses have been detected on other parts of the body, but are not as commonly seen as on the midline of the spine. A few have been noted on the head, attaching to the skull or the base of the ear. Another area of note is on the neck under the ear or on the front of the neck. Sometimes these can be dermoid sinuses and sometimes they are skin tabs.

The exact mode of the inheritance of the D.S. is not known. It is thought to be polygenic (multiple genes), rather than simple dominant or recessive. It has been noted that there can be carriers, or individuals that produce more dermoid sinuses than their littermates. Some lines are relatively D.S. free. Dogs that are subjects of D.S. are not candidates for a breeding program. The surgery removes the visual defect but not the genetic one. Pups having had surgery to remove a D.S. are eliminated from the conformation ring as per the AKC rules, which clearly state that a dog that has been surgically altered cannot compete.

The ethics of breeding require you to put the best possible representative of the breed out there. It should not only look like a Rhodesian Rideback, but it should be as healthy and sound as possible. As the D.S. is a very serious unsoundness, much thought should be given in your decision of the disposition of a D.S. puppy. If you decide to keep and operate on a D.S. subject, care must be taken to assure the pup of a home that will spay or neuter. Euthanasia is a permanent solution.

[Note: Because of the D.S., avoid injections in the area of the top of the neck and shoulders. Occasional reactions to vaccines can produce an inflammation that resembles a D.S.]

Dermoid Sinus – A Summary by E. Clough, V.M.D.
1010 Daniel Webster Highway
Merrimack , New Hampshire 03054

Introduction

Dermoid sinus (D.S.) was first used to describe the Rhodesian Ridgeback skin anomaly by Steyn, et al. This skin condition has also been called trichiasis spiralis, dermoid cyst, dermoid inclusion cyst and epidermal inclusion cyst. All of these terms have some applications; however, Dermoid, skin-like sinus, channel or fistula; (cyst means sac, i.e., not open to the surface) is most applicable. The Rhodesian Ridgeback Club of the U.S., Inc. prefers to use D.S. to describe the condition.

Description

No reports have been located which substantiate the author’s impression that D.S. has been found in other breeds. Dermoid sinus included in the ridge has been reported only once. They also occur in the sacral (rump) area and in this location are sometimes connected to the dura (spinal cord covering). This is not the case in the more common cervical (neck area) D.S. which connects the skin to the dorsal spinous ligament (the ligament which connects the top parts of the vertebrae). One or more D.S. may occur in the same animal. These sinuses are congenital (present at birth) and can be palpated (felt) as cords running between the skin and the spine. They form a small external opening which can be readily seen once the hair has been shaved.

Histologically (microscopically) the sinus is a thick-walled tube composed chiefly of fibrous tissue and lined with stratified squamous epithelium (skin cells). The surrounding connective tissue may or may not contain hair follicles, sebaceous glands and sweat glands which open into the lumen (hollow center) of the sinus. In uncomplicated cases the sinus is filled with sebum (oil), skin debris and hair. Once infected with bacteria the resulting inflammation and abscessation can lead to myelitis and encephalitis (swelling and infection of the spinal cord, its covering, and the brain). The reason for discrimination against animals with D.S. is the almost inevitable abscess which forms.

Heritability

Although not well understood, transmission of D.S. seems to be a dominant, polygenic problem with inconstant penetration. Another geneticist thinks that D.S. is due to a single completely recessive autosomal gene. This is not likely because normal parents do produce pups affected with D.S. Because of the genetic complexity and the difficulty in arranging, coordinating and collating the breeding studies necessary to prove the heredity of D.S., it is unlikely that we will be able to substantiate the exact mechanism of genetic transmission. There is a widely held belief that breeding Ridgebacks with D.S. produces an increased prevalence of pups with D.S. The R.R. Club of the U.S., Inc. believes that this could be substantiated if breeders had accurate records which could be collated and computed. It is our belief that careful controlled breeding studies would prove the inheritance of D.S. to be not only complex but also inter-related with other characteristics. Therefore, the likelihood seems to be remote that we will ever have Ridgebacks which are entirely free of D.S.

Because selective breeding will unquestionably reduce the prevalence of D.S., but probably not eliminate its occurrence, and because the condition results in difficult to treat abscesses unless surgically removed, it is our opinion and strong recommendation that dogs which have D.S. not be acceptable as show or breeding candidates. Surgical correction can be accomplished; however, culling at birth is a more humane way to handle the affected pups.

References

1. Antin, I.P.: Dermoid Sinus in a Rhodesian Ridgeback Dog. J.A.V.M.A., Vol. 157 No. 7, (1970): 961.
2. Burns, M. and M.N.Fraser: Genetics of the Dog. J.B.Lippincott Co., Philadelphia PA (1966): 84.
3. Hawley, T.C.: The Rhodesian Ridgeback Craft Press, Pretoria, S.A., (1957): 53.
4. Hofmeyr, C.F.B.: Dermoid Sinus in the Ridgeback Dog J.Small Animal Practice., Vol. 4. Suppl. (1957): 5-8.
5. Lord, L.H.; A.J.Cawley and J.Gilray: Mid-Dorsal Dermoid Sinuses in Rhodesian Ridgeback Dogs – A Case Report. J.A.V.M.A., 131 (1957): 515-518
6. Lutman, F.C.: How to Raise and Train a Rhodesian Ridgeback. T.F.H. Publications, Jersey City, NJ (1966).
7. Personal communications from numerous Rhodesian Ridgeback friends.
8. Severin, G.A.: Inheritable and Congenital Diseases in Dogs. Dog World (December 1974).
9. Steyn, H.P. J. Quinlan and C. Jackson: A skin Condition seen in Rhodesian Ridgeback Dogs: Report on two cases. J.S.A.V.M.A. X(4), (1939): 170-174.

Juvenile Myoclonic Epilepsy Rhodesian Ridgeback Type (JME)

Juvenile Myoclonic Epilepsy Rhodesian Ridgeback Type (JME) is an inherited disorder characterized by myoclonic jerks and photosensitivity. JME in Rhodesian Ridgeback dogs is a canine equivalent to the human form of JME, with which it shares the same symptoms and age of onset. These similarities made the canine equivalent of this disorder important study model and contributed to the identification of causative mutation.

Characteristics and Symptoms

Studied 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. Affected dogs are usually euthanized upon owner’s request.

Genetics

Juvenile Myoclonic Epilepsy in Rhodesian Ridgeback Dogs (JME) is caused by a 4-bp deletion in the exon 2 of the DIRAS1 gene, causing a frameshift and a loss of the stop signal. Research among other breeds affected with epilepsy revealed that this mutation is specific only for Rhodesian Ridgeback breed. A carrier rate of 15% was determined.

The expression of the DIRAS1 is limited to the brain and heart and it is suggested that DIRAS1 protein is needed for acetylcholine transmission at neuromuscular junctions and neuronal development. Nicotinergic cholinergic activity influences brain excitability and cognition, regulates the excitatory/inhibitory switch during neuronal development, stimulates glutamate release from thalamocortical terminals, and maintains nonrapid eye movement sleep by low levels of acetylcholine. Abnormal DIRAS1 function could alter cholinergic neurotransmission or formation of neuronal circuits and network assembly in the developing brain resulting in myoclonic epilepsy and photosensitivity.

Juvenile Myoclonic Epilepsy Rhodesian Ridgeback Type (JME)is inherited in an autosomal recessive pattern. Healthy parents of affected puppy are obligate heterozygotes and therefore carry one mutant allele. Heterozygotes have no symptoms. Dogs homozygous for the mutation will display the symptoms of the JME. At conception, when mating two carrier dogs, each cub has a 25% chance of being affected, a 50% chance of being an asymptomatic carrier, and a 25% chance of being unaffected and not a carrier.

Test Juvenile myoclonic epilepsy (JME)

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JME RR Test Results

Genocan & Ridgeback International Research Program
Test for ridge disposition in Rhodesian ridgeback

The Rhodesian ridgeback’s distinguishing feature is the ridge of hair running along its back in the opposite direction from the rest of its coat. This characteristic is genetically determined and governed by the dominant inheritance. To understand dominant inheritance, it is necessary first to realize that every dog has inherited from its parents, two copies of each gene (one from its mother and one from its father).

Dominant inheritance means that if the puppy inherited the ridge gen just from one parent, there ridge is formed on the puppy´s back. In this case, the dog with only one ridge gene is called heterozygote (Rr). If the dog inherited ridge gene from both parents, the dog has two ridge genes, will form a ridge on the back and is called dominant homozygote (RR).

However, in the litter there may ridgeless puppies. 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 .

However, according to the test results in practice, it appears that the ridge genetics in Rhodesian ridgebacks is not so simple and is characterized by incomplete manifestation of ridge gene. This means that all dominant homozygotes have ridge. Also, approximately 90% of the heterozygotes have ridge, but 10% of the heterozygotes are ridgeless. Very likely, the ridge gene is suppressed and ridge is not formed on the back. All individuals who lack ridge gene (rr) are ridgeless.

In collaboration with the Veterinary Research Institute in 2014, we have for the first time developed the genetic test, which distinguishes dominant homozygotes (two ridge genes) from heterozygotes (one ridge gene). This is the most accurate way how to predict birth of ridgeless puppies, if both parents are tested (see. Table below). Our test determines whether and to what extent there will ridgeless puppies in a litter!

Further, it was also observed the association between genetic disposition for the ridge and the occurrence of dermoid sinus. According to the research, dermoid sinus occurs approximately 5 times more often in dominant homozygotes. Our test may reduce the incidence of dermoids in Rhodesian Ridgebacks by a controlled selection of tested individuals for mating.

We have  developed the genetic test, which distinguishes dominant homozygotes (R/R – two ridge genes) from heterozygotes (R/r – one ridge gene). Using our genetic test, a breeder may accuratelly predict birth of ridgeless puppies (see Table below).

Test for ridge disposition in Rhodesian ridgeback