The Molecule of More

THE MOLECULE OF MORE

DO BIPOLAR GENES DRIVE IMMIGRATION?

I learned very quickly that when you emigrate, you lose the crutches that have

been your support; you must begin from zero, because the past is erased with

a single stroke and no one cares where you’re from or what you did before.

—Isabel Allende, writer

Bipolar disorder isn’t all or nothing. Some people have severe forms of
the illness and others have more mild forms. Some people have only
a bipolar tendency. We can see things in the personalities of this lat-
ter group that suggest unusually elevated moods, but not so bad that
we would diagnose them with a medical illness. It all depends on how
many risk genes a person inherits from her parents, and how much
vulnerability these genes confer. The genetic risk then interacts with a
person’s environment (a  stressful childhood, for  example), and the final 
product is some manifestation of bipolar disorder, or bipolar character-
istics not severe enough to cause the actual illness.
Is it possible that minor dysfunction in the dopamine transporter—
just  a  few  risk  genes or  genes that  have only a  mild effect—could give 
people “itchy feet,” so to speak? Might that play a role in the decision to
leave one’s home and seek new opportunities in a foreign country? It’s
not easy to pull up one’s roots, to say goodbye to friends and family, and
leave a community that’s familiar, comfortable, and supportive. Andrew
Carnegie, a nineteenth-century Scottish immigrant who started work-
ing in a factory for pennies a day and later became the richest man in
the world, wrote, “[the] contented do not brave the waves of the stormy
Atlantic, but sit helplessly at home.”
If bipolar genes promote emigration, these ambitious people would
carry their risk  genes with them, and  we  would expect to  find  high 
concentrations of bipolar genes in countries that have lots of immi-
grants. The United States is populated almost entirely by immigrants
and their descendants. It also has the highest rate of bipolar disorder:
4.4 percent, which is about twice the rate of the rest of the world. Are
the two related?