PROGRESSJapan, which has almost no immigration, has a bipolar rate of 0.7
percent, one of the lowest in the world. People in the United States with
bipolar disorder also start to have symptoms at a younger age, a marker
of a more severe form of the illness. About two-thirds develop symp-
toms before the age of 20, compared to only a quarter in Europe. That
supports the idea that the gene pool in the United States has a greater
concentration of high-risk genes.
The gene that tells the body how to make the dopamine transporter
is one of these genes, but there are many others. No one knows pre-
cisely how many, but it’s clear that some form of genetic inheritance is
playing a role. Children of bipolar parents are at least twice as likely
to develop bipolar disorder compared to the general population. Some
studies have found the risk to be ten times as high. But sometimes the
children get lucky. They get the advantages bipolar people enjoy with-
out getting the illness itself.
As noted, bipolar disorder isn’t all or nothing. Mood-disorder spe-
cialists talk about a bipolar spectrum. At one end of the spectrum is bipo-
lar I. People with this form of the illness experience severe mania and
severe depression. Next comes bipolar II. People with bipolar II experi-
ence severe depression, but more mild episodes of elevated mood called
hypomania (hypo means below, like a hypodermic injection that delivers
a drug underneath the skin). Farther down the spectrum is cyclothymia,
which is characterized by cycles of hypomania and mild depressive
episodes. Then there is something called hyperthymic temperament,
derived from the Greek word thymia, which means state of mind.
Hyperthymic temperament is not considered an illness. It doesn’t
occur in episodes like bipolar disorder. People with hyperthymic tem-
perament just have a “hyper” personality, and they have it all the time.
According to Hagop Akiskal, who did much of the pioneering work in
this area, people with hyperthymic temperaments are upbeat, exuber-
ant, jocular, overoptimistic, overconfident, boastful, and full of energy
and plans. They are versatile with broad interests, overinvolved and
meddlesome, uninhibited and risk-taking, and they generally don’t
sleep very much. They become overly enthusiastic about new directions
in their lives, such as diets, romantic partners, business opportunities,