Genetic and environmental influences on circulating NK and T cells and their relation to bipolar disorder.

BACKGROUND: In previous studies we found mild deficiencies of circulating T cells in patients with bipolar disorder (BD) and children at risk for BD, correlating to a higher inflammatory state. The genetic and environmental influences on these T cell deficiencies in association with BD development are unknown. OBJECTIVES: The aim is to quantify genetic and environmental factors that contribute to the association between the liability to develop BD and T cell deficiencies. METHODS: Participants of a Dutch bipolar twin study (11 monozygotic BD twin pairs, 15 dizygotic BD twin pairs, 15 monozygotic and 12 dizygotic healthy twin pairs) were included. A detailed FACS analysis of frozen stored leukocytes was carried out to determine the percentages of T cells and various other leukocyte and lymphocyte subsets. A bivariate liability threshold twin model was used to determine genetic and environmental (common and unique) influences on the correlation between BD and the various subsets. RESULTS: Lower percentages of T cells and higher percentages of NK cells were associated with the familial liability to develop BD. Neither genetic nor shared or unique environmental factors could explain the associations. Lithium usage explained part of the association for T cells, smoking in part that for NK cells. CONCLUSIONS: Our results confirm that BD is the result of a complex interaction between various genetic and environmental risk factors, in which T and NK cells act as important intermediate immune players.

The seroprevalence of antithyroid peroxidase antibodies in bipolar families and bipolar twins: results from two longitudinal studies.

BACKGROUND: Previous studies of our group among bipolar offspring and bipolar twins showed significant higher prevalence's and levels of antithyroid peroxidase antibodies (TPO-Abs) in offspring and co-twins (without a mood disorder) compared to controls, suggesting that TPO-Abs might be considered as vulnerability factor (trait marker) for BD development. OBJECTIVES: Here we elucidate, in the same cohorts, but now after 12- and 6-year follow-up, whether TPO-abs should be considered as a 'trait' marker for BD. The present study aims to investigate whether TPO-Abs (1) are stable over time, (2) are associated with lithium-exposure, (3) share a common genetic background with BD and are related to psychopathology. RESULTS: In bipolar offspring and twins, the prevalence of TPO-Abs is stable over time (r s = .72 p < .001 resp. r s = .82, p < .001) and not associated with lithium use. At follow-up, an increased prevalence of TPO-abs was again observed in bipolar offspring (10,4% versus 4%) and higher TPO-abs titers were still present in co-twins of bipolar cases compared to control twins [mean 1.06 IU/ml (SD .82) versus mean .82 IU/ml (SD .67)], although statistical significance was lost. CONCLUSIONS: Although our results show a trend toward an increased inherited risk of the co-occurrence of BD and thyroid autoimmunity, large-scale studies can only draw final conclusions. Nationwide epidemiological and GWAS studies reach such numbers and support the view of a possible common (autoimmune) etiology of severe mood disorders and chronic recurrent infections and autoimmunity, including thyroid autoimmunity.

A study of genetic and environmental contributions to structural brain changes over time in twins concordant and discordant for bipolar disorder.

This is the first longitudinal twin study examining genetic and environmental contributions to the association between liability to bipolar disorder (BD) and changes over time in global brain volumes, and global and regional measures of cortical surface area, cortical thickness and cortical volume. A total of 50 twins from pairs discordant or concordant for BD (monozygotic: 8 discordant and 3 concordant pairs, and 1 patient and 3 co-twins from incomplete pairs; dizygotic: 6 discordant and 2 concordant pairs, and 1 patient and 7 co-twins from incomplete pairs) underwent magnetic resonance imaging twice. In addition, 57 twins from healthy twin pairs (15 monozygotic and 10 dizygotic pairs, and 4 monozygotic and 3 dizygotic subjects from incomplete pairs) were also scanned twice. Mean follow-up duration for all twins was 7.5 years (standard deviation: 1.5 years). Data were analyzed using structural equation modeling software OpenMx. The liability to BD was not associated with global or regional structural brain changes over time. Although we observed a subtle increase in cerebral white matter in BD patients, this effect disappeared after correction for multiple comparisons. Heritability of brain changes over time was generally low to moderate. Structural brain changes appear to follow similar trajectories in BD patients and healthy controls. Existing brain abnormalities in BD do not appear to progressively change over time, but this requires additional confirmation. Further study with large cohorts is recommended to assess genetic and environmental influences on structural brain abnormalities in BD, while taking into account the influence of lithium on the brain.

The role of life events and psychological factors in the onset of first and recurrent mood episodes in bipolar offspring: results from the Dutch Bipolar Offspring Study.

BACKGROUND: Life events are an established risk factor for the onset and recurrence of unipolar and bipolar mood episodes, especially in the presence of genetic vulnerability. The dynamic interplay between life events and psychological context, however, is less studied. In this study, we investigated the impact of life events on the onset and recurrence of mood episodes in bipolar offspring, as well as the effects of temperament, coping and parenting style on this association. METHOD: Bipolar offspring (n = 108) were followed longitudinally from adolescence to adulthood. Mood disorders were assessed with: the Kiddie Schedule of Affective Disorders and Schizophrenia - Present and Lifetime Version or the Structured Clinical Interview for DSM-IV Axis I disorders; life events with the Life Events and Difficulties Schedule; and psychological measures using the Utrecht Coping List, Temperament and Character Inventory and short-EMBU (memories of upbringing instrument). Anderson-Gill models (an extension of the Cox proportional hazard model) were utilized. RESULTS: Life events were associated with an increased risk for first and, although less pronounced, subsequent mood episodes. There was a large confounding effect for the number of previous mood episodes; findings suggest a possible kindling effect. Passive coping style increased the risk of mood episode onset and recurrent episodes, but also altered the effect of life events on mood disorders. Harm avoidance temperament was associated with mood episode recurrence. CONCLUSIONS: Life events are especially a risk factor in the onset of mood disorders, though less so in recurrent episodes. Psychological features (passive coping and harm-avoidant temperament) contribute to the risk of an episode occurring, and also have a moderating effect on the association between life events and mood episodes. These findings create potential early intervention strategies for bipolar offspring.