Thyroid function (TSH levels)

Thyroid dysfunction is an important health problem that affects 10% of the population, increasing, above all, cardiovascular risk. Among other parameters, in clinical practice it is evaluated by measuring TSH levels, so that an increase would be related to hypothyroidism and a decrease to hyperthyroidism.

The thyroid is a bilobed, butterfly-shaped gland located in the neck in front of the trachea. It produces thyroid hormones, thyroxine (T4) and triiodothyronine (T3), which control the body's metabolism and the balance of other hormones. Among its many functions are the regulation of body temperature, heart rate, oxygen consumption and protein synthesis, hence they are essential in growth and organogenesis.

The thyroid is finely regulated by Thyroid Stimulating Hormone (TSH) secreted by the pituitary gland. TSH stimulates the release of thyroid hormones, but these, in turn, exert a negative action on TSH production when TSH levels increase.

Thyroid dysfunction is a very common condition. Moreover, in recent years it has become clear that not only clinical hypo- and hyperthyroidism have clinical manifestations, but that subclinical ones are associated with increased risk of pathological conditions such as coronary heart disease, depression or cardiovascular disease. More recently, studies have shown that even physiological variations of thyroid hormones within the normal range would be associated with many of these complications.

Therefore, knowledge of the factors that regulate this complex hormonal system can help in taking measures to reduce the risks associated with its dysregulation.

Alterations in thyroid function can trigger endocrine disorders and these alterations can be due to a multitude of factors ranging from heritable mutations to weight changes, atrial fibrillation, osteoporosis, etc. Based on a large meta-analysis of genome-wide association studies for thyroid function and dysfunction involving 55000 individuals, 42 loci associated with altered serum TSH levels were identified, of which 23 were previously reported markers and 19 markers were novel. Among the genes that seem to affect to a greater extent we can find PDE8B and PDE10A, which produce different phosphodiesterase enzymes for the hydrolysis of cyclic adenosine monophosphate phosphate (cAMP), an important regulator in many physiological processes.

Number of observed variants

13.5 million variants

Number of loci analyzed in the study

20 loci

Bibliography

Mayo clinic [March 2022]

Teumer A, Chaker L, Groeneweg S, et al. Genome-wide analyses identify a role for SLC17A4 and AADAT in thyroid hormone regulation. Nature Communications. 2018 Oct;9(1):4455.

Cooper, D. S. & Biondi, B. Subclinical thyroid disease. Lancet. 2012; 379, 1142–1154.

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