Okay, I am actually the one to blame for people thinking that the neural
crest genetic variant medical disorder ferrets get is WS, and I guess
that was something like 15 years ago.
 
Since then a classical geneticist who looked into it has noted that while
some may have their markings due to WS it is more likely that the neural
crest genetic variant, KIT oncogene is to blame.  One reason for saying
so is because of the body spotting/ body splotching also seen.  Since
that has been mentioned for years I hope more sites catch up.
 
That's not good news, actually.  Oncogenes can increase the malignancy
risk for an individual.  There are other risks as well.
 
To understand what is going on you need to know about fetal development.
This, BTW, relates to why the cells usually needed for stem cell research
are NOT from adults, nor from developed fetuses but from blastulas.  The
blastula is an early fetal stage when there is just a hollow ball of
cells.  There are no organs, there are no senses, there are no features.
In fact, what these are are the extra 8 day old fetal stage which is used
to impregnate women who are having fertility problems.  Using the extras
for stem cell research advances medical knowledge while keeping a number
of these from being thrown away as medical waste.  But, I am getting off
the point slightly.  The reason these cells are so useful for stem cell
research is because any tissue type would later derive from them.  That
point is essential for understanding neural crest discussions.  You see,
as time goes on, the fetus develops cell regions which are more
specialized so they have fewer types of cells they will later develop
into.  After a while one of these regions is the cardiac neural crest.
Later the cardiac crest which is responsible for things like cardiac
and some major vascular development separates from the neural crest
which provides head pigmentation, some ear structures, some intestinal
structures, some mandibular development, etc.
 
Now, if the mutation is for the cardiac neural crest cells then any of
the tissues which develop from this early fetal region MAY be affected.
Note that I say, "may".  These fetal cell genetic medical disorders
have what is called "variable expression".  That means that a person
can have a ferret parent who has a mild presentation but the offspring
might be severely affected.  This is why there is a higher rate of
certain cardiovascular problems, including both cardiomyopathy types, but
especially the harder to find (before death) hypertrophic cardiomyopathy.
(You can find some articles on this in the archives of Ferret-Genetics
in Yahoogroups and elsewhere.) Some of these circulatory problems result
in small litters due to reabsorbed dead fetuses, or litters with a number
of members who die soon after birth due to increasing the circulatory
malformation fetal death rate.  There can also be a higher newborn death
rate due to deaf ferret mothers not getting all of the signals they need
for rapid and correct responses.  Multiple breeders have discussed
encountering these problems, and there is a lot in the literature on this
in an assortment of mammals.
 
More commonly, the problem seems to be mutations affecting the neural
crest segment of cells after that splits from the cardiac crest.  These
can carry medical concerns for intestinal development, ear development,
mandibular (jaw) development, etc.
 
All of this may explain why it appears that ferrets with these genetics
tend to less commonly live to a previously very normal age of older than
late in the 6th year, and why it is important to start old age exams for
them earlier than you would for others.
 
These genetics were RARE in the U.S. a couple of decades ago and the
lifespans commonly seen were better, too.  Now-a-days, especially from a
number of ferret farms (although the push for these fancies first came
from private breeders and one mid-sized farm, many of which charged extra
for the marked kits) it is rare to encounter a ferret who does not have
extraneous white splotches such as panda heads, head blazes, body
spotting, or incomplete mitts or incomplete bibs.  All such markings are
neural crest variant markings.  The body markings are especially inclined
to be KIT oncogene ones.  (WS in mammals can cause the head markings but
does not tend to cause the body markings.) Right now breeders elsewhere
have a window in which they can educate and reduce the breeding for these
"fancies" to avoid the genetic time-bomb seem too often here.  Such
markings are present THROUGHOUT life rather than being roaning
(lightening which happens later in life).
 
BTW, I have found myself wondering after many discussions if knee patches
may at times have a different genetic cause.  Complete and cleanly
margined bibs seen with complete mitts (cleanly margined, full socks) in
which those normal dark portions on a standard are entirely de-pigmented
DO have a different genetic cause and that cause has never been
associated with any medical problems.  That is safe.  It is one reason
shows should separate the types in judging.
 
See the FML Archives (addy in the header of each day's FML),
the FHL Archives
<http://fhl.sonic-weasel.org>,
and Ferret-Genetics Archives
<http://groups.yahoo.com/group/Ferret-Genetics/>
[Posted in FML issue 4833]