Inheritance of syringomyelia in Cavalier King Charles spaniels
Clare Rusbridge BVMS DipECVN MRCVS
Susan P. Knowler BSc (Hons)
Stone Lion Veterinary Centre, 41 High Street, Wimbledon, London, UK SW19 5AU
neuro.vet@btinternet.com
tel 00 44 208 946 4228
fax 00 44 208 7860525
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 recognised 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–coloured CKCS
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because of the relatively small gene pool for recessive ruby colouration. 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 colour however selection for coat colour 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 colour. 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-colours were introduced to the ruby lines in an attempt to widen
the gene pool but still deliver some whole-colours. 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.
Current Breeding Advice
Giving breeding advice is limited by the large number of CKCS that are potentially carriers of the
condition
Affected Case
Identified by MRI (confirmed) or suspected on basis of clinical signs (scratching at shoulder area
when walking on leash or when excited) Not to be used at all for breeding.
Unaffected known carrier (sire or dam an affected case and all of it’s offspring ) will have
both genes. If mated with same will produce affected offspring (usually only one or two
offspring or may even ‘fail’).Only use very sparingly – i.e. retaining maximum possible variation
in the gene pool but not saturating it. Mate only with unrelated dogs who have had no
extended family history of the disorder (i.e. ancestors, half –siblings, etc)
Unaffected dog (it is likely that all modern CKCS will be carrier one or more of the genes).
Don’t use closely related dogs, line breed only on one side. Keep track of offspring – time of
onset can vary.
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