Re: Many symptoms of autism and Tourette are similar. Why?

Hi Alice,

You have made some very keen observations!  And no, these don't seem to be 
purely coincidental occurrences.

Without going into too much neurobiology, the neurotransmitter dopamine 
(sometimes abbreviated "DA"), is involved in many different aspects of 
behavior.  In my field of study, I look at dopamine because it is related to 
reward and drug abuse, but dopamine is also very important in motor 
functions and the control of movement.

A number of recent studies (see list below) have suggested that there is a 
significant genetic or biological relationship between ADHD and Tourette's 
syndrome (among many others).  A recent study from Cambridge (England) 
suggested that at least 8% of children with autism also were diagnosed with 
Tourette's syndrome.  Moreover, interviews with families suggested that 
there were other family members who also had this same diagnosis -- 
supporting a heritable role for the transmissions of these disorders.

Baron-Cohen, S, Mortimore, C, Moriarty, J, Izaguirre, J, & Robertson, M.
The prevalence of Gilles de la Tourette's syndrome in children and 
adolescents with autism.  Journal of Child Psychology and Psychiatry, Vol 
40, pp 213-218. Feb 1999.

Kerbeshian, J., Burd, L., May 1996.
Case study: Comorbidity among Tourette's syndrome, autistic disorder and 
bipolar disorder (note: bipolar disorder is the new term for what used to be 
called manic depression). Journal of the American Academy of Child and 
Adolescent Psychiatry, vol 35, pp 681-685.

Sverd, J. (May 1991)
Tourette syndrome and autistic disorder: a significant relationship.
American Journal of Medical Genetics, vol 39, pp 173-179.

I don't know if this next part will bore you with too much detail -- but you 
appear to have a good grasp on what is going on, so I suspect you have 
already done a good bit of reading on the topic (so perhaps I can point you 
in new directions).

Transmitters bind to receptors (in a sortof lock & key analogy) on neurons 
in the brain (and all over the body).  The receptor is a protein that our 
cells produce (as directed to by our DNA) -- so one thing that some 
scientists focus on is identifying the receptors that seem to bind these 
neurotransmitters.  One specific type of dopamine receptor -- the dopamine 
D2 receptor (or DA-D2 for short) has been suggested to play a role in a 
number of neuropsychiatric disorders.  Some studies suggest that one gene 
that contributes to DAD2 receptor occurs *more frequently* in some disorders 
(in a 1991 study, this gene was found in 45% of Tourette's patients, 46% of 
patients with ADHD, 54% of autistic patients,  43% of alcoholics, and 45% of 
patients with post-traumatic stress disorder (PTSD)).  But there were also 
many disorders that weren't correlated with this gene -- including: obesity, 
parkinson's disease, depression, or panic attacks.

It's hard to believe that one gene would cause all these things --however, 
it isn't hard to believe that one gene may play some modulatory role -- 
especially since many of them seem to share the neurotransmitter dopamine to 
some degree (drug abuse & alcoholism, tourette's syndrome, autism, etc).

This last paper is:

Comings, DE, Comings, BG, Muhleman, D., Dietz, G., Shahbahrami, B....and a 
handful of others.... (Oct 1991).
The dopamine D2 receptor locus as a modifying gene in neuropsychiatric 
disorders. Journal of the American Medical Assn (JAMA for short), vol 266,
pp 1793-1800.

note that this is a *very* controversial topic (that one gene does so much),
and you would be well served to read the letters to the editor that followed 
in subsequent issues (Oct 2, 1991; Feb 5, 1992) to get a more balanced
perspective.

If you were unaware, you can access many scientific journals through the 
Medline database.  It is on the web (and free) at:
     www.ncbi.nlm.nih.gov/PubMed/medline.html

I hope this helps answer your question.
Feel free to email if you like to discuss this further.

Cheers,

Josh Rodefer, Ph.D.
Harvard Medical School
josh_rodefer@hms.harvard.edu