A molecule that receives a thyroid hormone and permits it to dock on the nuclear membrane of a cell. The thyroid hormone receptors (THRs) belong to a family of nuclear receptors that function as hormone-activated transcription factors and act by modulating the expression of genes. THRs bind DNA in the absence of hormone, usually suppressing the transcription of genes. Hormone binding involves a conformational change in the receptor that lets it to activate transcription.
There are two THR genes — alpha and beta — and the primary transcript for each gene can be alternatively spliced, generating different alpha and beta receptor isoforms. Four different thyroid hormone receptors are recognized — alpha-1, alpha-2, beta-1 and beta-2. The different forms of THRs are expressed differently by tissue and by developmental stage. For example, the alpha-1 receptor is the first isoform expressed in embryonic life. And there is a great increase in expression of beta receptors in the brain shortly after birth.
The syndrome of thyroid hormone resistance is due to mutations in the beta THR gene which abolish its capacity to bind other molecules. The syndrome is characterized by a form of hypothyroidism with goiter (enlargement of the thyroid gland), elevated blood levels of T3 and thyroxine (two thyroid hormones) and normal or elevated blood levels of TSH (thyroid stimulating hormone). More than half of children with the syndrome have attention deficit disorder. The disorder is transmitted as an autosomal dominant trait.
- Torsion fracture
A fracture, also called a spiral fracture, in which a bone has been twisted apart.
The most common of the focal dystonias, a state of excessive or inadequate muscle tone in the muscles in the neck that control the position of the head. Torticollis can cause the head to twist and turn to one side. The head may also be pulled forward or backward. Torticollis can occur at any age, […]
- Torticollis, congenital
A deformity of the neck that is present at birth. Congenital torticollis is due to shortening of the neck muscles. Congenital torticollis tilts the head to the side on which the neck muscles are shortened, so that the chin points to the other side. The shortened neck muscles are principally supplied by the spinal accessory […]
An act by which severe pain or suffering, whether physical or mental, is intentionally inflicted on a person, for a purpose such as obtaining information or a confession, punishment, intimidation or coercion, or for any reason based on discrimination of any kind. Survivors of torture often suffer from physical and psychological symptoms and disabilities. There […]
- Torus fracture
A fracture in which one side of a bone bends but does not actually break. Torus fractures normally heal on their own within a month, with rest and disuse. Also known as incomplete fracture or buckle fracture.