Genes and Common Diseases: Major psychiatric disorders in adult life

Psychiatric disorders are common. The World Health Organization (WHO) estimates that at least one in four people will experience a clinically significant episode of psychiatric illness at some point in their lives. Although most such disorders are short lived and do not result in specialist care many cases become disabling and the WHO Global Burden of Disease Study (Murray and Lopez, 1997) has estimated that in health economic terms unipolar depression (UPD) vies with cardiovascular disease as the leading cause of disability in adults world wide. Schizophrenia and bipolar affective disorder (BPD) are also major public health problems which feature in the WHO's top ten of economically burdensome diseases. Between them, the affective disorders (UPD and BPD) and schizophrenia also account for over 60% of completed suicides. Therefore we will here focus on these three conditions as the main exemplars of common complex psychiatric disorders with substantial genetic contributions. Clinical features and epidemiology Unipolar depression (UPD) is so called because it consists of episodes of depressed mood whereas bipolar disorder (BPD) presents as episodes of both mania and depression. (A minority of patients with bipolar disorder have episodes of mania and no depressive episodes, but in terms of course, outcome, treatment response and pattern of illness in relatives they resemble typical bipolar disorder cases and are therefore classified as such rather than a “unipolar mania”).