Hello!
Before
I answer I must preface by saying that the specific genetics of TS have
not yet been identified, although the research is making progress. For
example, it is now finally accepted within the establishment that TS
is NOT the result of a dominant gene (in other words, TS is not due
to a single gene that manifests in every individual that carries it).
Comings in 1990 wrote an excellent book (TS and Human Behaviour) arguing
that the genetics were considerably more complicated than this, but
until the Human Genome Project completed its analysis without finding
evidence of this dominant gene other professionals were not willing
to consider Coming's work.
The most
recent reports I've heard (at the end of 2000) were from the Tourette
Syndrome Association International Consortium for Genetics -- this consortium
is comprised of 12 sites across the US (largely Yale, California, and
Rochester) and Canada (Toronto). These researchers discuss promising
'leads' in areas 4q and 8p of the genome. Each of these sites received
Maximum Likelihood Scores greater than 2 -- this means that there is
a 99% chance these sites are meaningful, although more data is needed.
In general, these researchers now believe that TS may be caused by 3-5
major genes.
Having
said that, the genetic model that best fits the available evidence FOR
NOW is the THEORY that TS is a semi-dominant, semi-recessive trait.
In other words if an individual carries one or more of the relevant
genes, (s)he MAY or MAY NOT show symptoms of TS or associated disorders
(the genes appear to have 50% penetrance, which means that half the
time when you carry the gene you show it).
The idea
is that the TS genes are additive, like genetic lego. If mom carries
a gene (50% of the time showing it) and dad carries a gene (50% of the
time showing it) and both pass on these genes, they come together to
create TS in the child.
As you
can see, then, the genetics are complicated and according to current
theories THERE ARE NO GUARANTEES YOUR CHILD WILL OR WILL NOT HAVE TS
EVEN IF YOU YOURSELF HAVE TS. Let's say for argument's sake BOTH you
and your partner have TS. You have a 50% chance of passing on your genes,
and your spouse has a 50% chance of passing on her genes. Even assuming
that both genes will be penetrant in the child (which is not a certainty),
there is only a 25% chance that the child will have full-blown TS (although
the odds are higher that the child will have some associated symptoms
--learning/attention difficulties, anxiety, etc.).
The final
thing I should mention is that there are many individuals with TS (I
count myself among them) who intend to have children regardless of what
the genetics end up being. From my own perspective I see the immense
number of very desirable qualities these genetics bring to an individual,
and I know that I, having and understanding the neurology myself, would
be the best possible parent for a child with TS and/or associated disorders.
Finally, my experience has been that the environment I was in, the reactions
I received, and the attitude I formed were the MOST crippling aspects
of this 'disorder' for me. These are things that I am now aware of and
can help my child avoid.
In fact,
I'm quite excited about passing on a legacy -- if I had a 'normie' for
a son or daughter I don't think I'd know what to do with him/her!!!
:-)
I hope
this helps -- all the best to you.
Dr. Dunc.
