Dermoid Sinus 

The Dermoid Sinus is a sinus, which connects the skin with the dura mater (outer covering of the spinal cord) in the vertebral canal or other structures in the area. It is a congenital (present at birth) and hereditary (transmitted from parent to offspring) abnormality in Rhodesian Ridgeback dogs and Thai Ridgeback Dogs. The word "dermoid" means skin like and the word "sinus" means channel, recess or cavity.

Dermoid Sinus is classified into 4 types depending on the depth to which it penetrates, with Type I penetrating only through the skin and Type IV reaching the spinal cord (this is rare). Dermoid sinus occurs only rarely in dogs that aren't Ridgebacks or Ridgeback crosses.

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.
D.S Pups coult be a great Pet not for breeding. 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 in the Rhodesian Ridgeback

Nicolette Salmon Hillbertz, M.Sc., PhD student

Dept. of Animal Breeding and Genetics, section of Molecular Genetics, Swedish University
of Agricultural Sciences

Abstract

This research program aims to identify the causative mutation/mutations for dermoid sinus (DS) in Rhodesian Ridgeback. Unique possibilities to evaluate and study hereditary factors of DS, with focus on the Swedish Rhodesian Ridgeback population, are present and currently utilized. Specific objectives are (i) to perform a genome wide scan using available genetic markers, (ii) discover genetic markers in order to identify disease-causing mutations and (iii) DNA-based typing of individuals using available and novel polymorphic genetic markers to identify carriers of disease-causing mutations. A long-term objective is the development of breed-specific genetic markers to allow inter-breed utilization of a DS-specific DNA-test.

Introduction

A literature survey was initiated in 2002, with focus on available scientific publications concerning DS. The literature survey is frequently updated. In addition, an inter-species comparison was conducted and revealed that the condition DS is also found in humans where it is associated with the disease Spina Bifida occulta, which is classified as a Neural Tube Defect (NTD) (Bajpai et al., 1997).

Facilities and Research Environment

The laboratory is located at the Uppsala Biomedical Centre (BMC), which is a leading Life Science Centre in Sweden. The department research group has an excellent track record in both basic and applied research on farm and companion animals. This is particularly well exemplified in the identification of both the causative mutation for canine leukocyte adhesion deficiency (Kijas et al., 1999) and a mutation regulating IGF2 expression. causing increased muscle growth in the pig (van Laere et al., 2003) that were achieved in our laboratory. The laboratory is thus, well equipped and suited to pursue molecular genetic research.

Preliminary Studies

A population genetic study has been performed, utilizing the Swedish Rhodesian Ridgeback register, which has provided a suggestion of the mode of inheritance of DS (n=1040 offspring) (Salmon Hillbertz, 2005) and the dorsal ridge-trait (n=2806 offspring) (Salmon Hillbertz & Andersson, 2005).
Blood samples from a number of affected and related phenotypically normal dogs have been collected. Genomic DNA and RNA derived from DS tissue have been prepared and PCR will be used to amplify candidate genes. The collection of field material is conducted continuously. In addition, a whole-genome scan will be performed, utilizing the collected DNA samples from the Swedish Rhodesian Ridgeback population. All assemblages of field material have been performed in accordance with the animal ethics regulations of the Swedish National Board for Laboratory Animals and the Swedish Board of Agriculture.
A candidate gene for DS, has been selected and successfully PCR amplified from Rhodesian Ridgeback genomic DNA and RNA derived from DS tissue. The nucleotide sequence has been determined. Searches of the available dog genome sequence data bases were performed and the candidate gene was not found in the current dog data bases. Probes and primers have been designed that allow expression analyses of dermoid sinus and control tissues. Nucleotide sequences of the candidate gene, from phenotypically normal and affected Rhodesian Ridgebacks will be conducted in order to identify possible polymorphisms. Identification of polymorphism in the candidate gene will allow DNA-based typing of the Rhodesian Ridgeback population. In addition, preliminary results show that we have identified expression of the candidate gene in postnatal dermoid tissue. According to the NCBI-database (www.ncbi.nih.gov), this has previously not been described.
An ongoing pilot project is conducted with the aim to evaluate different clinical methods that could be adequate for diagnosis. Currently, we have been able to clinically identify DS in tissue underlying the skin of Rhodesian Ridgebacks with one method. From the DS-positive Rhodesian Ridgebacks brought to the Swedish University of Agricultural Sciences (SLU), DS
localization, direction and extension have been clinically identified in approximately 50%. An efficient clinical diagnosis method may result in accurate and illuminating information concerning DS extension, thus creating possibilities of reducing unnecessary culling of DS-positive Rhodesian Ridgeback offspring.
Derived DS tissue samples from affected Rhodesian Ridgebacks are currently undergoing histology preparation. The samples will be utilized for the study of DS morphology with microscope equipment.

Research plan

The research plan within this project includes strategies such as:
Identification of candidate genes for Dermoid Sinus using comparative genetic PCR-based methods
A whole genome scanning approach will be pursued based on available polymorphic markers covering the domestic dog genome
Identification of polymorphic genetic markers within or in the vicinity of candidate genes, in order to perform SNP-based haplotype studies.
Nucleotide sequences for candidate genes isolated from affected and phenotypically normal dogs will be determined.
Obtained nucleotide sequences will be analysed for mutations and polymorphisms.
Genotyping of DS affected and non-affected individuals.

Miscellaneous

All participation of breeders/owners will be treated in a confidential manner.

Glossary

Allele
One of two or more alternative forms of a gene that occur at the same locus.
Candidate gene
A gene, located in a chromosome region suspected of being involved in a disease, whose protein product suggests that it could be the disease gene in question.
DNA
The molecule that encodes genetic information. DNA is a double-stranded molecule held together by weak bonds between base pairs of nucleotides. The molecule that encodes genetic information. DNA is a double-stranded molecule held together by weak bonds between base pairs of nucleotides.
Gene
Physical and functional unit of hereditary that carries information from one generation to the
next.
Genome
The total genetic constitution of an organism
Haplotype
The particular combination of alleles in a linked group encoded by genes in close vicinity on the same chromosome.
Inter-species
Between species
Locus
The site or location on a chromosome occupied by a gene.
Nucleotide
A single unit that makes up the DNA or RNA.
PCR
Polymerase Chain Reaction. A technique that allows amplification of specific DNA segments in a short time.
Phenotype
The observable traits or characteristics of an organism, for example hair colour, weight, or the presence or absence of a disease. Phenotypic traits are not necessarily genetic.
Primer
A short oligonucleotide sequence used in a polymerase chain reaction (PCR).
Polymorphisms
Presence of discreetly different forms of a gene or a character.
SNP
Single nucleotide polymorphism. A single nucleotide change in the DNA code.
Whole genome scanning
A continuous genome-wide mapping which may enable identification of candidate genes for phenotypic traits or disease phenotypes.

References

Bajpai M, Kataria R, Gupta D K & Agarwala S. 1997. Occult spinal dysraphism. Indian J Pediatr Nov-Dec; 64 (6 Suppl). 62-7.
Kijas J M, Bauer T R Jr, Gafvert S, Marklund S, Trowald-Wigh G, Johannisson A, Hedhammar A, Binns M, Juneja R K, Hickstein D D & Adersson L. 1999. A missense mutation in the beta-2 integrin gene (ITGB2) causes canine leukocyte adhesion deficiency. Genomics 61: 101-107.
Van Laere A-S, Nguyen M, Braunschweig M, Nezer C, Collette C, Moreau L, Archibald A L, Haley C S, Buys N, Andersson G, Georges M & Andersson L. 2003. Positional identification of a regulatory mutation in IGF2 causing a major QTL effect on muscle growth in the pig. Nature 425: 832-836.
Salmon Hillbertz, N H C. 2005. Inheritance of dermoid sinus in the Rhodesian Ridgeback. The Journal of Small Animal Practice 46; 71-74.
Salmon Hillbertz N H C & Andersson G. 2005. Autosomal dominant mutation causing the dorsal ridge predisposes for Dermoid sinus in Rhodesian ridgeback dogs. Accepted The Journal of Small Animal Practice.