Between the poles.
The prevalence of bipolar disorders is approximately 1 % of the population (12-month prevalence). Men and women are equally affected. The first episode usually occurs between the ages of 15 and 30. However, years often pass before the diagnosis of bipolar disorder is made, as initially only depressive episodes tend to occur and it only becomes clear at a later stage (with the first manic episode) that it is not a unipolar recurrent disorder but a bipolar disorder. Genetic vulnerability plays an important role in the development of manic-depressive illness. However, it is ultimately the gene-environment interaction that determines whether certain genes are 'activated' or not and whether a particular disorder becomes clinically manifest in later life or not (vulnerability-stress model). Twin studies (identical genetic material), for example, show that both twins need not necessarily develop bipolar disorder.
Depressive and manic episodes in bipolar disorders occur both in (variously rapid) alternation and in a mixed state. Both depressive and manic episodes may also be accompanied by psychotic symptoms. Precise classification and diagnosis are made by a psychiatrist.