Cohort effect shows earlier and stronger effects of bipolar disorder
Researchers observe a cohort effect for earlier age at onset of bipolar disorder. Bipolar disorder is also more common in patients with a family history of unipolar depression and bipolar disorder.
A cohort effect suggests an earlier age at onset of bipolar disorder and greater burden of psychiatric disorders in 2 generations of direct progenitors of patients, according to a study in the Journal of Clinical Psychiatry.
Robert M Post, MD, from the Bipolar Collaborative Network in Bethesda, Maryland, and colleagues, examined whether patients who were younger at age of entry to the Bipolar Collaborative Network had an earlier age at onset compared with those who were older at entry. They also hypothesized that younger patients at entry would have a higher total burden of unipolar depression and bipolar disorder as well as other mental illnesses in their parents and grandparents.
A total of 968 outpatients with a mean age of 41 years with bipolar disorder including bipolar I, bipolar II, and schizoaffective, from 4 cities in the United States (Dallas; Cincinnati; Los Angeles; and Bethesda) and 3 in Europe (Urtecht, the Netherlands; and Freiburg and Munich, Germany) completed self-rated questionnaires on their retrospective course of illness, demographics, stressors in childhood, and age at onset of bipolar disorder. The diagnoses rated included unipolar depression, bipolar disorder, history of suicide, attempt or completed suicide, alcohol abuse, drug abuse, and “other illnesses.” The same ratings were also included for assessment of both maternal and paternal grandparents, any of the parents' siblings, and any of the parents' children. The study was conducted from 1995 to 2002.
The researchers found that patients who were younger at the time of their network entry (representing the most recent birth cohorts) had an earlier age at onset of their bipolar illness compared with those who were older at entry. Relatives from earlier cohorts, or relatives of patients who were older at entry, had lesser amounts of psychiatric illness than relatives of the younger patients (most recent cohorts).
Regarding the findings, Dr Post stated, “The resulting likely increase in severity of bipolar illness in future generations based on this earlier age at onset and increased familial loading, particularly in the United States, deserves focused clinical and public health attention and attempts at amelioration.”
Post RM, Kupka R, Keck PE, et al. Further evidence of a cohort effect in bipolar disorder: more early onsets and family history of psychiatric illness in more recent epochs. J Clin Psychiatry. dx.doi.org/10.4088/JCP.15m10121