For Broman, making that diagnosis may not have been hard since the condition, as Ketter puts it, "is hugely familial." Broman herself is bipolar, though her illness was not diagnosed until adulthood. Children with one bipolar parent have a 10% to 30% chance of developing the condition; a bipolar sibling means a 20% risk; if both parents are bipolar, the danger rises as high as 75%. About 90% of bipolars have at least one close relative with a mood disorder.

For all that, when the disorder does appear in a child, the diagnosis is often wrong. ADHD is the likeliest first call, if only because some of the manic symptoms fit. The treatment of choice for ADHD is Ritalin, a stimulant that has the paradoxical ability to calm overactive kids. But giving Ritalin to a bipolar child can deepen an existing cycle or trigger one anew. Brandon Kent, a 9-year-old from La Vernia, Texas, in whom ADHD was diagnosed in kindergarten (they did not yet know he was bipolar), took Ritalin and paid the price. "It sent him into depression," says his mother Debbie Kent. "Within a couple of months, he was flat on the couch and wouldn't move." By some estimates, up to 15% of children thought to have ADHD may actually be bipolar.

	Some scientists believe that nearly half of the children previously thought to be depressed may instead be bipolar.

Similar misdiagnoses are made when parents and doctors observe symptoms of the low phase of the bipolar cycle and conclude that a kid is suffering from simple depression. Treat such a child with antidepressants like Prozac, however, and the rejiggering of brain chemistry may trigger mania. Some researchers believe that nearly half of all children thought to be depressed may really be bipolar.

For most kids, the consequences of not identifying the illness can be severe, since the bipolar steamroller gets worse as children get older. Though they tend to be verbally skilled and are often creative, bipolars find school difficult because the background noise of the disorder makes it hard for them to master such executive functions as organizing, planning and thinking problems through. The most serious symptoms may appear when kids reach age 8, just when the academic challenge of grade school starts to be felt. "They're being asked to do things that they're very poor at," Papolos says, "and it's a blow to their self-esteem." If school doesn't kick the disorder into overdrive, puberty often does, with its rush of hormones that rattle even the steadiest preteen mind.

Still, all these natural stressors and the new awareness of the disorder may not be enough to account for the explosion of juvenile bipolar cases. Some scientists fear that there may be something in the environment or in modern lifestyles that is driving into a bipolar state children and teens who might otherwise escape the condition.

One of the biggest risk factors is drugs. People with a genetic predisposition to bipolar disorders live on an unstable emotional fault line. Jar things too much with a lot of recreational chemistry, and the whole foundation can break away, especially when the drugs of choice are cocaine, amphetamines or other stimulants. "We do think that use of stimulating drugs is playing a part in lowering the age of onset," says Hirschfeld.

Stress too can light the bipolar fuse. Many latent emotional disorders, from depression to alcoholism to anxiety conditions, are precipitated by life events such as divorce or death or even a happy rite of passage like starting college. And bipolar disorder can also be set off this way. "Most of us do not think environmental stress causes the disorder," says Dr. Michael Gitlin, head of the mood-disorders clinic at UCLA. "But it can trigger it in people who are already vulnerable."

A decidedly more complicated explanation may be gene penetrance; not every generation of a family susceptible to an illness develops it in the same way. Often, later generations suffer worse than earlier ones because of a genetic mechanism known as trinucleotide repeat expansion. Defective sequences of genes may grow longer each time they are inherited, making it likelier that descendants will come down with the illness. This phenomenon plays a role in Huntington's disease and could be involved in bipolar. "There's a stepwise genetic dose that can increase the risk," theorizes Ketter.

The first part of determining how those genes work is figuring out where they are hiding, and the National Institute of Mental Health is looking hard. Investigators at eight research centers around the country, working under an NIMH grant, are studying the genomes of 500 families with a bipolar history to see what genetic quirks they share. So far, at least 10 of the 46 human chromosomes have shown irregularities that may be linked with the condition. The most interesting is chromosome 22, which has been implicated not only in bipolar disorder but also in Schizophrenia and a little-known condition called Velo-Cardio-Facial syndrome, which has Schizophrenia links as well. The seeming relatedness of disorders that so prominently feature delusions has not been lost on researchers, though with so much still unknown about chromosome 22—to say nothing of the other nine tentatively linked with bipolar—no one is ready to draw any conclusions. "There are probably genetic variants that cut across multiple systems in the brain," says Dr. John Kelsoe, psychiatric geneticist at the University of California, San Diego.

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