There has always been anecdotal interest in the coexistence of 'great wits and madness', and in the familial aspects of both genius and mental illness, but it is only in recent years that systematic studies have been made of groups of gifted artists, especially writers. They are relevant to our subject. In summary, they show that such groups have very high rates of manic-depressive psychosis, especially bipolar illness.
Schizophrenia is entirely absent.
In the families of those gifted individuals the relatives have high rates of creativity, not necessarily literary, and high rates of affective disorder. These rates are higher in siblings but also significant in the parents of creative individuals. All were distinguished writers, some household names. The writers had a substantially higher rate of mental illness, predominantly affective, with a tendency towards bipolar attacks. There was also a higher prevalence of affective disorder and creativity in the writer's first degree relatives, suggesting that these traits run together in families and may be genetically connected.