Tyrosine hydroxylase deficiency is a rare inherited neurological disorder that is caused by deficiency of the enzyme tyrosine hydroxylase, which is important for the production of a group of chemical messengers. This condition has two forms. Symptoms of the mild form usually appear in the first year of life. These include unusual positioning of limbs, muscle stiffness, and gait disturbanceand may be prevented or treated by L-dopa supplement. Without treatment, individuals become wheelchair bound. The severe form appears soon after birth and is less responsive to L-dopa treatment. Symptoms in this form are similar to the mild form and may also affect involuntary body functions such as body temperature and blood pressure. Some affected individuals have intellectual disability, speech problems and psychiatric disturbances. Tyrosine hydroxylase deficiency is caused by pathogenic variants in the TH gene.