TH

The TH gene provides instructions for making the enzyme tyrosine hydroxylase, which is important for normal functioning of the nervous system. Tyrosine hydroxylase takes part in the first step of the pathway that produces a group of chemical messengers (hormones) called catecholamines. Tyrosine hydroxylase helps convert the protein building block (amino acid) tyrosine to a catecholamine called dopamine. Dopamine transmits signals to help the brain control physical movement and emotional behavior. Other catecholamines called norepinephrine and epinephrine are produced from dopamine. Norepinephrine and epinephrine are involved in the autonomic nervous system, which controls involuntary body processes such as the regulation of blood pressure and body temperature.

tyrosine hydroxylase deficiency - caused by mutations in the TH gene

More than 20 mutations in the TH gene have been identified in people with tyrosine hydroxylase (TH) deficiency. These mutations result in reduced activity of the tyrosine hydroxylase enzyme. As a result, the body produces less dopamine, norepinephrine and epinephrine. These catecholamines are necessary for normal nervous system function, and changes in their levels contribute to the abnormal movements, autonomic dysfunction, and other neurological problems seen in people with TH deficiency.

other disorders - associated with the TH gene

Other variations in the TH gene may also modify catecholamine production, which affects the risk of developing conditions associated with regulation of the autonomic nervous system. In particular, certain common TH gene variations (polymorphisms) affect the extent to which blood pressure increases with stress, and may increase the risk of high blood pressure (hypertension).

The most common TH gene variation among people of European descent, called allele *9.3, has been identified in a larger percentage of babies who die from sudden infant death syndrome (SIDS) than in other babies. This version of the gene may affect the regulation of breathing or arousal in infants.