context: Doctors don't completely understand the causes of bipolar disorder. But they've gained a greater understanding in recent years of the bipolar spectrum, which includes the elated highs of mania to the lows of major depression, along with various mood states between these two extremes. Bipolar disorder seems to often run in families and there appears to be a genetic part to this mood disorder. There is also growing evidence that environment and lifestyle issues have an effect on the disorder's severity. Stressful life events -- or alcohol or drug abuse -- can make bipolar disorder more difficult to treat. Experts believe bipolar disorder is partly caused by an underlying problem with specific brain circuits and the functioning of brain chemicals called neurotransmitters. Three brain chemicals -- noradrenaline (norepinephrine), serotonin, and dopamine -- are involved in both brain and bodily functions. Noradrenaline and serotonin have been consistently linked to psychiatric mood disorders such as depression and bipolar disorder. Nerve pathways within areas of the brain that regulate pleasure and emotional reward are regulated by dopamine. Disruption of circuits that communicate using dopamine in other brain areas appears connected to psychosis and schizophrenia, a severe mental disorder characterized by distortions in reality and illogical thought patterns and behaviors. The brain chemical serotonin is connected to many body functions such as sleep, wakefulness, eating, sexual activity, impulsivity, learning, and memory. Researchers believe that abnormal functioning of brain circuits that involve serotonin as a chemical messenger contribute to mood disorders (depression and bipolar disorder). Many studies of bipolar patients and their relatives have shown that bipolar disorder sometimes runs in families. Perhaps the most convincing data come from twin studies. In studies of identical twins, scientists report that if one identical twin has bipolar disorder, the other twin has a greater chance of developing bipolar disorder than another sibling in the family. Researchers conclude that the lifetime chance of an identical twin (of a bipolar twin) to also develop bipolar disorder is about 40% to 70%. In more studies at Johns Hopkins University, researchers interviewed all first-degree relatives of patients with bipolar I and bipolar II disorder and concluded that bipolar II disorder was the most common affective disorder in both family sets. The researchers found that 40% of the 47 first-degree relatives of the bipolar II patients also had bipolar II disorder; 22% of the 219 first-degree relatives of the bipolar I patients had bipolar II disorder. However, among patients with bipolar II, researchers found only one relative with bipolar I disorder. They concluded that bipolar II is the most prevalent diagnosis of relatives in both bipolar I and bipolar II families. Studies at Stanford University that explored the genetic connection of bipolar disorder found that children with one biological parent with bipolar I or bipolar II disorder have an increased likelihood of getting bipolar disorder. In this study, researchers reported that 51% of the bipolar offspring had a psychiatric disorder, most commonly major depression, dysthymia (low-grade, chronic depression), bipolar disorder, or attention deficit hyperactivity disorder ( ADHD). Interestingly, the bipolar parents in the study who had a childhood history of ADHD were more likely to have children with bipolar disorder rather than ADHD. In other findings, researchers report that first-degree relatives of a person diagnosed with bipolar I or II disorder are at an increased risk for major depression when compared to first-degree relatives of those with no history of bipolar disorder. Scientific findings also show that the lifetime risk of affective disorders in relatives with family members who have bipolar disorder increases, depending on the number of diagnosed relatives. Along with a genetic link to bipolar disorder, research shows that children of bipolar parents are often surrounded by significant environmental stressors. That may include living with a parent who has a tendency toward mood swings, alcohol or substance abuse, financial and sexual indiscretions, and hospitalizations. Although most children of a bipolar parent will not develop bipolar disorder, some children of bipolar parents may develop a different psychiatric disorder such as ADHD, major depression, schizophrenia, or substance abuse. Environmental stressors also play a role in triggering bipolar episodes in those who are genetically predisposed. For example, children growing up in bipolar families may live with a parent who lacks control of moods or emotions. Some children may live with constant verbal or even physical abuse if the bipolar parent is not medicated or is using alcohol or drugs. Some findings show that people with bipolar disorder have a genetic predisposition to sleep-wake cycle problems that may trigger symptoms of depression and mania. The problem for those with bipolar disorder, however, is that sleep loss may lead to a mood episode such as mania (elation) in some patients. Worrying about losing sleep can increase anxiety, thus worsening the bipolar mood disorder altogether. Once a sleep-deprived person with bipolar disorder goes into the manic state, the need for sleep decreases even more. In one study, researchers interviewed 39 bipolar patients with primarily manic or depressed episodes to determine the presence of social rhythm disruptions during the two months prior to the onset of the mood. ( A social rhythm disruption is a disturbance in daily routines such as sleeping, eating, exercising, or interacting with other people, which in turn could affect patterns of brain activity tied to mood regulation.) When comparing the results with volunteers in the control group, researchers concluded that most people with bipolar disorder experience at least one social rhythm disruption prior to a major mood episode. In addition, the researchers found that social rhythm disruption affected more bipolar patients with mania than the patients with depression. Their findings concluded that 65% of the patients with bipolar disorder had at least one disruption in their daily rhythm in the eight weeks before the onset of a manic episode. Talk to your doctor if you have difficulty falling asleep or maintaining sleep. There are several non-addictive sleep medicines available that can help resolve sleep problems. Also, cognitive behavioral therapy has been shown to be a helpful treatment for patients with bipolar disorder who have poor sleep or anxiety and fears about poor sleep.