In some recent posts I pointed to suggestive evidence of various forms of
brain involvement and dysregulation in the pathogenesis and pathophysiology
of cancer and autoimmune diseases. I mentioned that breast cancer seemed to
differentiate itself from other cancers in this regard on epidemiological
grounds.
Several weeks ago, the Mayo Clinic published an epidemiological study of
breast cancer conducted in Iowa. The results were quite interesting. The
incidence of breast cancer varied quite considerably for women of Northern
European origin. Those of Irish descent had the lowest rates, while those
of Swedish descent had the highest rates. Surprisingly, those of Irish
descent had the highest familial rates, while those of Swedish descent had
the lowest familial rates.
There is another disease for which being Swedish and female is highly
significant - multiple sclerosis. This shows up as part of the latitude
effect - the disease is almost endemic in northern Sweden. Of course many of
the possible causal variables are so highly correlated that it is not
possible with our current limited knowledge to determine causal pathways.
As examples of other correlations for which we have no current understanding
of there full implications, I would point out that many biological pigments
are derived from tyrosine along the dopamine synthesis pathway. There are
also other unusual correlations involving dopamine - the incidence of
schizophrenia in a population increases by about 10% when there is an
influenza epidemic in the 6th month of pregnancy. But schizophrenia
liability has also been recently strongly correlated with a polymorphism of
the nicotinic acetylcholine receptor. One way that dopamine comes in is that
activation of this receptor as by cigarette smoking, causes an increase in
brain dopamine, because the neuromodulatory pathways arising from the
various brain stem nuclei are strongly interdependent.
I would also like to mention the case of type II diabetes. Here we also
have epidemiological heterogeneity. The subset of patients who are females
of northern European descent are well characterized by Cloninger's brain
model, which accounts as well for many other possible comorbid conditions in
both the index patient and relatives. Cloninger's model points to genetic
variations in dopamine and serotonin pathways as underlying these conditions
See:
Cloninger, C. R. (1987b). Neurogenetic adaptive mechanisms in
alcoholism. Science 230: 410-416.
Cloninger, C. R. (1988). A unified biosocial theory of personality
and its role in the development of anxiety states: a reply to
commentaries.
Psychiatric Developments 6(2): 83-120.
Alan J. Robinson
robin073 at tc.umn.edu
