Tyrosine Hydroxylase Deficiency

Gene : TH

What is Tyrosine hydroxylase deficiency?

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.

How is Tyrosine hydroxylase deficiency inherited?

Tyrosine hydroxylase deficiency is inherited in an autosomal recessive manner. This type of inheritance requires the presence of two copies of a pathogenic variant in the gene for a person to have the genetic disease. Both parents must be carriers of a pathogenic variant in the gene in order to be at risk to have an affected child. The child must inherit a pathogenic variant from each carrier parent in order to be affected. There is a 1 in 4 chance that a baby will inherit two mutated copies of the gene and be affected when both parents are carriers.

What does it mean to be a carrier?

There are generally no signs or symptoms associated with being a carrier for tyrosine hydroxylase deficiency. The risk to have a child affected with tyrosine hydroxylase deficiency is increased. Testing of reproductive partners is recommended for carriers of tyrosine hydroxylase deficiency.

How common is Tyrosine hydroxylase deficiency?

The prevalence of Tyrosine hydroxylase deficiency is unknown. Fewer than 100 patients have been described worldwide to date.

Family References and Resources
Clinician References
What is Analyzed?
  • Full gene sequencing
Affected Systems




GI Tract

Carrier Rates
Detection Rate
Carrier Frequency
General Population > 99% 1 in 167

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