This is the summary provided for breeders and pet owners. Other breeds are being investigated so the focus is not only on cavaliers, but no other breed has been found to have such high rates of CM, and therefore be so predisposed to SM as the cavalier.
Lay summary
Syringomyelia (SM) is a painful condition, more common
in toy breeds, including the Cavalier King Charles Spaniel
(CKCS), than other breeds. In these toy breeds, SM is
usually secondary to a specific malformation of the skull
(called Chiari-like Malformation, CM for short).
There has been debate as to whether head shape is related
to CM/SM, especially as some humans have similar
characteristic facial and skull shapes, and what this may
be. Identifying a head shape in dogs that is associated
with these diseases would allow for selection away from
these conditions and could be used to further breeding
guidelines.
Dogs were measured in several countries using a standardised
“bony landmark” measuring system and photo
analysis by trained researchers.
This paper describes two significant risk factors associated
with CM/SM in the skull shape of the CKCS: extent
of brachycephaly (the broadness of the cranium (top of
skull) relative to its length) and distribution of doming
of the cranium.
The study showed that having a decreased cephalic
index (less brachycephaly) was significantly protective.
Further to this, more cranium at the back of the head
(caudally) relative to the amount at the front of the head
(rostrally) was significantly protective against disease development.
This was shown at three and five years of
age, and also when comparing a sample of “SM clear”
individuals over five years to those affected under three
years.
This study suggests that brachycephaly, with resulting
rostrocaudal doming, is associated with CM/SM. These
results could provide a way for selection against the risk
head shape in the CKCS, and thus enable a reduction in
CM/SM incidence. Studying other breeds in which CM
free individuals are more frequent may validate this risk
phenotype for CM too.