TSHB

The TSHB gene provides instructions for making a protein subunit of a hormone called thyroid stimulating hormone (TSH). Thyroid stimulating hormone consists of two subunits called alpha and beta. The TSHB gene provides instructions for making the beta (B) subunit of thyroid stimulating hormone. The alpha and beta subunits are bound together to produce the active form of the hormone. A particular segment of the beta subunit, known as the buckle or seatbelt, wraps around the alpha subunit to form the functional hormone.

Thyroid stimulating hormone is made in the pituitary gland, a gland at the base of the brain. This hormone plays an important role in the growth and function of the thyroid gland, a butterfly-shaped tissue in the lower neck. It also stimulates the production of thyroid hormones, which play a critical role in regulating growth, brain development, and the rate of chemical reactions in the body (metabolism). The pituitary gland monitors levels of thyroid hormones. When thyroid hormone levels are too low, the pituitary gland releases thyroid stimulating hormone into the bloodstream. Thyroid stimulating hormone, in turn, signals increased thyroid gland growth and production of thyroid hormones.

congenital hypothyroidism - caused by mutations in the TSHB gene

Researchers have identified several TSHB mutations that alter the size or shape of the thyroid stimulating hormone beta subunit. Many of these mutations affect the beta subunit's seatbelt region, which holds the alpha subunit in place and stabilizes the hormone's structure. Some mutations severely shorten the beta subunit, eliminating the seatbelt region partially or entirely. Other mutations change the chemical building blocks (amino acids) used to make the beta subunit. As a result, the seatbelt region cannot buckle around the alpha subunit. TSHB mutations prevent the production of functional thyroid stimulating hormone or its release (secretion) from the pituitary gland. As a result, thyroid hormone production is not stimulated, leading to low hormone levels that are characteristic of congenital hypothyroidism. Additionally, the thyroid gland is reduced in size (hypoplastic) because its growth is not stimulated.