Lack of confirmation of thyroid endophenotype in Bipolar Disorder Type I and their first-degree relatives

Among the biological factors associated with the development and outcomes in Bipolar Disorder Type I (BD-I), previous studies have highlighted the involvement of both thyroid function and/or auto-immunity, proposing a thyroid endophenotype. The objective of this study was to determine the presence of thyroid alterations in BD-I and their first-degree relatives (FDR).

Unselected, cross-sectional case-control study with parallel analysis of individuals affected by BD-I (239), their FD-R (131), and 108 healthy controls. Thyroidal functional abnormalities (TSH and free T4) and thyroidal antibodies (thyroglobulin and thyroperoxidase antibodies) were studied. Assessments were carried out in parallel. The sample was described using arithmetic means, standard deviations, percentages and ranges. Chi-square, Student-t tests, ANOVA and Pearson correlation coefficients were used when indicated.

BD-I on actual and/or ever treated with lithium showed significant thyroidal functional abnormalities as compared to their FD-R and healthy controls. This BD-I subgroup showed a significant greater proportion of subjects suffering from subclinical hypothyroidism (22%). The role of gender/lithium interactions was relevant. The groups did not show differences in terms of positivization of thyroidal antibodies.

The crosssectional design and the lack of determination of dietary iodine deficiencies and/or thyroidal ecographical controls may be a drawback.

The present study supports previous findings on the effect of lithium treatment on thyroidal functional, but did not support previous findings related to a familial association or endophenotype. In addition, the present study did not support a familial aggregation of thyroidal antibodies positivization in pedegrees of BD-I.