Syringomyelia is a common condition in the Cavalier King Charles spaniel (CKCS). The problem is caused by an overly small occipital bone, part of the back of the skull. This means that the cavity in the skull containing the back of the brain is too small and the surrounding fluid (the cerebrospinal fluid) cannot circulate freely. The fluid is forced into the spinal cord creating a cavity called syringomyelia. The resulting damage to the spinal cord results in the typical signs of this condition of which the most common is shoulder scratching especially when excited or walking on a lead. The scratching is typically to one side only but may become bilateral. There is no evidence of skin or ear disease. Affected dogs are also sensitive around the head, neck and forelimbs and often cry/yelp/scream for apparently no reason. Pain may be related to head posture and some dogs prefer to sleep or eat with their heads up. Some severely affected young dogs develop a neck scoliosis i.e. their neck is twisted. Some dogs may develop a wobbling hind limb gait and / or and a forelimb weakness. Signs are usually recognized between 6 months and 3 years however dogs of any age may be presented.

Recently a family tree of over 4,200 related dogs was constructed from the pedigrees of 100 dogs with syringomyelia. For comparison a family tree from 40 CKCS with primary epilepsy and no clinical signs of syringomyelia was also constructed. The epilepsy pedigrees had been amassed by a dedicated member of the UK CKCS Club over a period of 15 years. Study of the two family trees resulted in the following conclusions.

The modern CKCS breed has a smaller gene pool than 15 years ago and can be traced back predominantly to a relatively small group of dogs and their closely breed descendants. The earliest point that all 100 syringomyelia cases came together was a bitch, coded G that had only one litter of two offspring in 1959. These offspring formed part of relatively small selection of stud stock used by the major breeders of the 60's and 70's from which many of the modern champions have emerged. All syringomyelia cases could be traced back through to Bitch G, through significant ancestors C, D, M and S not only through both the dam and the sire, but at least 6/8 great grandparents. In addition particular matings produced high numbers of affected individuals suggesting Bitch Z, born in 1957, was also significant to the condition. At least three out of four grandparents of all syringomyelia cases could be traced to Bitch Z. The lines were sometimes independent from descendant lines from Bitch G. Thus all 8 great-grandparents of affected cases were varying combinations of descendants of Bitch G or Bitch Z or (more usually) both. As a consequence it is suggested that the inheritance is likely to involve 2 or more genes.

There is a tendency for more severe disease and earlier onset with increased line breeding. For example, a three month old CKCS that was euthanatised because of hydrocephalous had 32/32 great-great-great-grandparents descended from the significant lines, which included champions known to have a tendency for shoulder scratching whilst walking. There appears to be 3 forms of the disease based on severity and age of onset 1) Puppies with hydrocephalous 2) juvenile form (presenting at 6-15 months) with scoliosis (twisted neck) and weakness 3) adult form (1-10years) initially presenting with shoulder scratching and pain secondary to syringomyelia. Another trend is that the sire and dam might develop disease after the offspring i.e. the offspring had a more severe disease which developed first, then signs would become apparent in the sire or dam (or both).

The family tree of idiopathic epilepsy was a different subset of the CKCS population although there was some overlap. Epilepsy is particularly a problem in whole-colored CKCS because of the relatively small gene pool for recessive ruby coloration. Although the majority of the primary epilepsy group had bitch G in the ancestry, only 30% of cases were descended from bitch G via dogs C, D, M or S compared to 100% of 6/8 great grandparents for syringomyelia cases.

The disease is not linked to coat co lour however selection for coat color variation is believed to have influenced the development of the disease as certain significant ancestors for syringomyelia are also important in the inheritance of coat color. The disease is most common in Blenheim and Rubies which are recessive coat variations and must be bred from a more restricted gene pool. Fifteen years ago, tri-colors were introduced to the ruby lines in an attempt to widen the gene pool but still deliver some whole-colors. This appears to have been important in the history of syringomyelia by increasing the cohort of dogs with genes from both G and Z. The popularity of certain champions and continued line breeding has increased the number of dogs with genes from G and Z. Avoidance of some lines which carry certain diseases e.g. heart and cataract disorders is also affecting the incidence of syringomyelia by narrowing the gene pool further. As the condition is found in all the popular lines it will be extremely difficult to "breed it out" from study of the family tree. Indeed to do so might increase the incidence of other diseases. Therefore the most appropriate way forward is to collect samples of DNA from normal, abnormal and related CKCS with a view to identifying the gene(s). Ideally the same process would occur concurrently for heart disease. Ultimately this information could be used to allow dogs carrying a tendency towards heart disease or syringomyelia to be safely mated and allow that line to be continued and the incidence of the disease to decrease.

Syringomyelia update
July 19, 2003

Genetic information for breeders who wish to help prevent this disease.
There is now good evidence that the disorder is caused by two or more recessive genes . Unfortunately, there is no easy way to know whether a dog is normal or is a syringomyelia carrier. MRI will only identify an affected case. The only way to distinguish between normal and carriers without knowing the genes is for accurate information about cases and litters for each individual dog over a period of 3 generations. Unfortunately this is impractical, and now too late! However, once the gene/s have been identified then it is possible to have a blood test for Syringomyelia. This is therefore the quickest way forward, but it will still take a long time.

Possible inheritance for Syringomyelia
Assume two recessive genes "g" and "z" cause Syringomyelia. Normal, dominant genes would be "G" and "Z." An affected case would only occur if both sire and dam carry both g and z genes and each pass them on. A Syringomyelia case only has "g" and "z" so is pure breeding. It can only pass on "g" and "z" genes so all its offspring, no matter what match, will inherit both these genes. The dam / sire and all offspring of a syringomyelia case are called known carriers.

• Syringomyelia cannot be 'bred out' without knowing the genotype (i.e. finding the genes).
• To find a gene you need DNA from a range of normal and affected dogs and known carriers. This is always done in confidence. No one but the geneticists need know which dog is which
• Blood is the best source of DNA because it is a convenient large quantity and collected for all sorts of tests (cholesterol, hormones, etc) Geneticists can use this spare blood to search for genes.
• A cheek swab is another source but it is more difficult to collect the DNA from it.
• When the genetic testing becomes available please cooperate by obtaining and submitting samples for testing.
• Geneticists may wish to have whole family groups to help identify particular genes so please be prepared for this.