Bipolar risk is mostly genetic—yet twins still diverge
Heritability estimates reach 70–90 percent, but identical twins share the diagnosis only about 40 percent of the time versus roughly 5 percent for fraternal pairs. Lifetime prevalence sits near 1–3 percent, with manic and depressive poles lasting days to weeks.
Bipolar disorder, once called manic depression, swings between low periods and stretches of unusually high mood that may run for days, weeks, or occasionally months. Severe elevation with psychosis is mania; milder elevation that does not wreck functioning is hypomania. Manic phases bring surplus energy, euphoria or irritability, impulsivity, and sleep loss; depressive phases bring crying, bleak outlook, and withdrawn demeanor. Bipolar I requires at least one manic episode; bipolar II requires hypomania plus major depression without full mania; cyclothymia mixes hypomanic symptoms with subthreshold depressions. Drug- or illness-induced mood swings are not diagnosed as BD.
Mechanisms remain incompletely mapped. MRI studies show differences in risk-reward and emotion-regulation regions; cortisol and HPA-axis work links stress biology to manic phases. Genetics may explain up to 70–90 percent of risk, while concordance is about 40 percent in identical twins versus about 5 percent in dizygotic twins. Environment adds child abuse, chronic stress, and traumatic bonding; ADHD also raises bipolar risk, and early maltreatment tracks earlier onset and worse prognosis. Six- to twelve-month prevalence is about 1 percent; lifetime prevalence 1–3 percent; pediatric estimates near 3.9 percent under some criteria. Onset ages cluster around 24 or 46 in a bimodal pattern.
Treatment centers on mood stabilizers—especially lithium—plus anticonvulsants such as lamotrigine and valproate, and atypical antipsychotics for acute mania or when stabilizers fail. Psychotherapy improves course; antidepressants for bipolar depression are contested because some classes can spark mania. About 58–68 percent of people with bipolar I experience psychosis in mood episodes, while co-diagnosis of schizophrenia is low (about 8 percent). Roughly 40–60 percent of people with BD are employed, yet over 80 percent may miss work for psychiatric reasons across five years. Mania lasts over a week by DSM-5; hypomania at least four consecutive days. The disorder is intermittent poles on a highly heritable but incomplete genetic lottery.
Source: Bipolar disorder
