

Scientific American
Ask An Expert
"Is there a biochemical test that accurately
diagnoses bipolar disorder? I heard on the
radio today that millions of people in the U.S.
have bipolar disorder and that 75 per cent of
them are undiagnosed and untreated."
- -James R. Spradling, Oro Valley, Arizona
The following response comes from Fred Petty, the director
of the Mental Health Clinic at the Dallas Veterans
Administration Medical Center and profesor of psychiatry
at the University of Texas Southwestern Medical School:
"The current best estimate is that adult lifetime prevalence of
bipolar disorder in the U.S. is about 1 percent for severe
cases and 2 to 3 percent if milder cases are included--cases
that would include cyclothymia and 'bipolar 2.' Given the
population of the U.S. (about 250 million), those numbers
translate into about two to three million with severe bipolar
disorder and some five to seven million total, including those
with mild symptoms. So the figures you heard on the radio
seem reasonable."
"I have seen estimates that two thirds to three quarters of
the people with depression are undiagnosed and untreated.
I haven't seen the corresponding statistics for bipolar
disorder, but I would say that, looking at mood disorders
overall, most patients are still undiagnosed and untreated."
"Right now the diagnosis of bipolar disorder is a clinical
diagnosis, which means it is made by a physician based on
information about the patient's symptoms, mental status and
medical history. It is important that people obtain a medical
evaluation, because there are some conditions, such as
thyroid disease, which can mimic the symptoms of bipolar
disorder."
"There is, at present, no routinely available biochemical
diagnostic tests for bipolar disorder. My laboratory has
published some work looking at the blood levels of an
amino acid called GABA (gamma amino butyric acid),
which functions as a neurotransmitter in the brain. Bipolar
patients often show low levels of GABA in the
bloodstream. The GABA test is currently used only for
research purposes; GABA levels appear abnormal only in
about one third of the patients who are bipolar. Also, this
test is not specific for bipolar, because low GABA levels
are also found in people exhibiting non- bipolar depression."
"One of the likely reasons that GABA is not a universal
indicator is that bipolar disorder is heterogeneous. In other
words, the syndrome we call 'bipolar' actually results from
several different causal conditions (etiologies); it is possible
that in some cases the low GABA level is the predominant
etiology, but not in all. In this sense, bipolar is somewhat
like diarrhea--we call it one thing, but you can get it a
variety of ways (through colitis, food poisoning, and so
on)--or like heart failure, which has a multiple etiology. But
low GABA readings look useful because the anomaly
persists even after the person improves clinically. If my
group can get its grants renewed, we would like to look at
GABA levels in children whose parents have bipolar
disorder."
"There is also some very interesting work being done with
PET scans, which can show deficits of the neurotransmitter
serotonin in the brain, associated with depression. Serotonin
deficits seem to persist even after the depression
lifts--suggesting that it is a real biological marker. PET scans
of serotonin in bipolar patients have not yet been done, to
my knowledge. Brain imaging using magnetic resonance has
been applied to bipolar research; some bipolar patients
show brain lesions in these images."
"Another very exciting area of investigation involves the
search for a genetic locus for bipolar illness. Bipolar is
probably the most genetic of all psychiatric illnesses, and
psychiatric illnesses in general have a strong genetic
component. If you have one parent with the illness, you face
a 25 percent risk; if both parents are bipolar, you face a 50
percent risk. Among identical twins, there is an 80 percent
concordance for bipolar disorder. Ideally, we would like to
diagnose the illness in young people before they express any
severe symptoms. In this way, we could save a lot of human
suffering; the earlier a patient gets into treatment, the better
the prognosis."
DISCLAIMER