Is SM Hereditary?
Is SM hereditary? The answer may seem obvious -- that it is -- but doubts have been raised. In Bet Hargreaves' October 2005 update of her Syringomyelia Blog on http://www.cavaliers.co.uk/articles/...hargreaves.htm she questions whether SM is due to genes or genetic factors. She writes:
"Is Syringomyelia hereditary? Why I ask the question has it been proved scientifically in Cavaliers that Syringo is hereditary is because in a veterinary paper published in 2004, it was stated by the researchers into the problem in Cavaliers all the affected Cavaliers researched had at least 6 of 8 Gr-grandparents that could be traced back to a common female ancestor born in 1956, whereas only 6.6% of unaffected Cavaliers had this ancestry.
"There has now been a list published of Cavaliers who have been M.R.I scanned and are showing no sign of SM but at least 6 of 8 of their Gr-grandparents also can be traced back to the same common female ancestor born in 1956. To add further doubt as to whether SM has been proved to be hereditary in Cavaliers, researchers at Duke University, America into the human form of the same condition for around 3 years, say that it will be at least several more years yet before it can be said as to whether it is due to genes or genetic factors. Because of this information, for the benefit of the Cavalier breed, should the first priority be to prove that SM is hereditary in Cavaliers."
Then, in Dr. Dewey's October 2005 article in JAVMA (along with Drs. Bergm Barone, Marino, and Stefanacci), they state: "There is strong evidence to suggest that COMS is a heritable condition in Cavalier King Charles Spaniels." They cite earlier articles by themselves, Clare Rusbridge, Penny Knowles, and Drs. Lu, Pfeiffer, and Targett as authorities for the evidence.
As a layman, on one hand, I wonder why anyone would doubt that SM is hereditary, considering the wide range of lines of Cavaliers with either SM or COMS or both. But then, even the neurologists currently studying the disorder -- Drs. Dewey et al -- only go so far as to say that there is "strong evidence" to suggest it. What does it take to tip the scales toward or away from heritability?
Orlando, Florida USA
I think any scientist will only say "strong evidence" until a direct genetic link is ascertained. That can't be done until the genome scan is done, but the reason the breed was accepted for the genome scan was on the basis of extremely strong evidence (really beyond a reasonable doubt) that this is hereditary and genetically linked.
Bet Hargreaves also introduces the red herring of human SM -- which is meaningless, as is comparing the skull malformation type of SM with SM caused by spinal cord deformations... just because the end result is the spinal fluid pockets, you cannot assume relationships between cause or between species. In addition the human form is EXTREMELY rare and the population is very small for study (and obviously there are far greater limits in how studies can be conducted on human patients as opposed to dogs), whereas the cavalier population with SM shows every sign of being enormous (which is of course whey the cavalier research is of such interest to human SM researchers).
As the genome scan is now getting underway we will know within a year if it is hereditary as some clear markers should turn up fairly quickly, according to the main molecular geneticists doing the scan. Then maybe the editorials can move on to some other consideration -- such as whether the breed clubs should work to introduce low cost MRI schemes. ;)
karlin - Thanks for replying concisely (and w/o the flaming emotion I would have introduced) exactly what I would have said.
S M hereditary
Please explain the difference between genes and genetic factors. Aren't genetic factors caused by genes and don't both fall under the heading of hereditary?