The Role of Thyroid Dysfunction in Alzheimer's Disease: A Systematic Review and Meta-Analysis

Imbalances in thyroid hormones have been linked with Alzheimer's dementia. Several studies have reported an association between thyroid disorders, such as hyper- or hypothyroidism, with Alzheimer's disease. However, there remains no consensus about the precise role of thyroid dysfunction in Alzheimer's disease. In this study we systematically searched PubMed, Embase and Scopus for clinical studies which reported the prevalence of hyper- or hypothyroidism in people with Alzheimer's disease compared to controls. Meta-analysis was performed to compare thyroid disorder prevalence in Alzheimer's disease and controls. Subgroup analysis was performed to assess the clinical and subclinical thyroid dysfunction, separately. Seven studies, including 1189 people with Alzheimer's disease and 72711 controls, were included in our sample. Hypothyroidism was significantly more prevalent in Alzheimer's disease compared with controls (6.4% vs 2.4%, p=0.01). Subgroup analysis showed that clinical hypothyroidism was not significantly different between Alzheimer's disease compared to controls (10.0% vs 5.3%, p=0.35). There was no difference in the crude overall prevalence of clinical and subclinical hyperthyroidism in Alzheimer's disease versus controls (2.4 vs 1.9%, p=0.73). Our analyses revealed a higher prevalence of hypothyroidism in Alzheimer's disease. Whether this finding is explained by hypothyroidism being a risk factor for, or consequence of, Alzheimer's disease requires longitudinal analysis. Our review supports further work into a potential role for treatment of hypothyroidism in the prevention or delay of Alzheimer's disease.

Shedding light on thyroid hormone disorders and Parkinson disease pathology: mechanisms and risk factors

Parkinson's disease (PD) is a neurodegenerative disorder characterized by loss of dopaminergic neurons. Dopaminergic system is interconnected with the hypothalamic-pituitary-thyroid axis. Dopamine (DA) upregulates thyrotropin releasing hormone (TRH) while downregulating thyroid stimulating hormone (TSH) and thyroid hormones. Moreover, TRH stimulates DA release. PD is associated with impaired regulation of TSH and thyroid hormones (TH) levels, which in turn associate with severity and different subtypes of PD, while levodopa and bromocriptine treatment can interfere with hypothalamic-pituitary-thyroid axis. Thyroid disturbances, including hypothyroidism, Hashimoto's thyroiditis (HT), hyperthyroidism and Graves' disease (GD) not only increase the risk of PD but also share some clinical signs with PD. Also, several genes including RASD2, WSB1, MAPT, GIRK2, LRRK2 and gene products like neurotensin and NOX/DUOX affect the risk for both PD and thyroid disease. Hypothyroidism is associated with obesity, hypercholesterolemia, anemia and altered cerebral blood flow which are associated with PD pathology. Herein we provide a comprehensive view on the association between PD and thyroid hormones regulation and dysregulations, hoping to provide new avenues towards targeted treatment of PD. We performed a comprehensive search in literature using Pubmed and Scopus, yielding to a total number of 36 original articles that had addressed the association between thyroid hormone disorders and PD.

Brain pathway differences between Parkinson's disease patients with and without depressive symptoms

Introduction

Depression occurs frequently in patients suffering from Parkinson's disease (PD). However, the neural basis of depression in PD remains unclear. Diffusion magnetic resonance imaging (DMRI) connectometry is based on the spin distribution function (SDF), which quantifies the density of diffusing water.

Aim

The aim of this study was to assess the microstructural changes in the brain connectivity of PD patients with and without depressive symptoms.

Methods

DMRI was used to assess microstructural abnormalities in the brains of 16 PD patients with depressive symptoms compared to 11 PD patients without depressive symptoms. Data used in the preparation of this paper were obtained from the Parkinson's progression markers initiative (PPMI) database (http://www.ppmi-info.org/data/). This dataset was acquired on a 3-Tesla scanner (Siemens), producing 64 DWI at b = 1000 s/mm2 and one b0 image. Diffusion MRI data were corrected for subject motion, eddy current distortions, and susceptibility artefacts due to magnetic field inhomogeneity. DMRI connectometry was conducted in a total of 27 patients using percentage measurement.

Results

PD Patients with depressive symptoms showed decreased anisotropy (FDR < 0.05) in the fornix bilaterally, left inferior longitudinal fasciculus (ILF) and corticospinal tract bilaterally compared to PD patients without depressive symptoms.

Conclusions

Lesser WM integrity of the left ILF fibers, which connect visual face recognition areas to the amygdala and hippocampus, seems to be associated with depressive symptoms in PD patients. Our study supports the hypothesis that neurodegenerative processes in projections from the somatosensory, cingulate, and insular cortices may be related to depression in PD.

Disclosure of interest

The authors have not supplied their declaration of competing interest.

Worldwide survey of AIDS vaccine challenge studies in nonhuman primates: vaccines associated with active and passive immune protection from live virus challenge

An AIDS Vaccine Surveillance System (AVSS) was designed and implemented to track the rapidly growing international database supporting the development of promising AIDS vaccines. Both preclinical nonhuman primate (NHP) and clinical human trials are tracked by the AVSS. This report presents summary data generated from the AVSS on the NHP AIDS vaccine/live virus challenge studies only. Summary data on more than 100 preclinical HIV/SIV vaccines are presented within the framework of 1) 13 arbitrary Vaccine Types, 2) studies grouped by animal model (i.e., chimpanzee/HIV-1, and macaque/SIV, HIV-2), and 3) immunization approach (i.e., active and passive). Systematic and timely presentations of these summary data, both here and in future reports, aim to promote a clearer understanding of both earlier and more recent preclinical AIDS vaccine developments.