ESPE Abstracts (2015) 84 S1.1

The Effect of Thyroid Hormones on the Brain

Joanne Rovet

Toronto, Canada

Background: It is long been known that thyroid hormone (TH) is essential for brain development; however most evidence is based almost on rodent models. Since the advent of advanced neuroimaging techniques, it is now possible to study the manifestations of TH role in developing human brain.

Objective and hypotheses: To examine findings from structural and functional MRI investigations of maternal hypothyroidism and congenital hypothyroidism (CH), which represent two human conditions involving a loss of TH at different stages of gestation and early life. We hypothesize that different brain regions have unique critical periods of TH need.

Method: Participants were offspring of women with hypothyroidism in pregnancy (HYPO), children with CH, and controls with normal thyroid history, aged 10–14 years. All received extensive testing and structural and functional MRIs. Scans were examined for size of hippocampus (H) and corpus callosum (CC), cortical thickness, and fMRI response.

Results: HYPO and CH show i) reduced size and atypical functioning of H, albeit in different hemispheres, ii) different patterns of cortical thinning and thickening, iii) abnormalities in different CC segments. Results are associated with weaknesses in memory, visual and verbal processing, and executive functions.

Conclusion: As in rodents, the human brain critically needs TH for its early development while the particular processes that are disrupted by TH loss and their specific brain locations reflect the exact timing of the TH insufficiency. These findings have implications for specific weaknesses in cognitive functioning as well as everyday functional limitations.

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