Some startling statistics: In a sample of 70 'unaffected' CKCS MRI scanned for breeding purposes in Europe and North America:
49 (70%) had syringomyelia
12 (17%) were at risk -young dogs with occipital hypoplasia but no syringomyelia yet
9 (13%) were clear
Other screening studies have reported 'more with than without'. Pedigree analysis confirms this is a worldwide problem and not limited to any particular country, breeding line or kennel.
The newsletter also notes:
What has the investigation into the disorder has shown so far:
A number of dogs have a mild malformation but do not have syringomyelia
Clinically affected offspring often have affected (clinically or sub-clinically) parents
Clinically affected parents can produce 'clear' offspring
The signs of syringomyelia can get worse and have an earlier onset with each generation
Chiari malformation occurs occasionally in other toy breeds ( the DNA collection includes 7 different breeds)
Syringomyelia can be asymptomatic or apparently asymptomatic. Sometimes this is because the signs of pain are not recognised e.g. many dogs show discomfort during the evening and on walks. If the dogs are predominantly penned and not exercised (as in some breeding establishments) then signs of pain may be missed. However some dogs genuinely exhibit few or no signs because of where and how their spinal cord has been affected
Length and diameter of the syrinx does not necessarily reflect severity and should not be used as a factor in decision making for breeding.
The inheritance of the disorder is not yet known. The 'best guesses' are that it is polygenic or dominant with incomplete or variable penetrance but the influence of another gene cannot be ruled out; affected lines are always found on both sire and dam sides of an affected case