Abstract
Tyrosine hydroxylase (TH) is a tetrahydrobiopterin (BH4) dependent enzyme that catalyses the conversion of L-tyrosine to L-dopa, the rate-limiting step in the biosynthesis of dopamine. Autosomal recessive mutations in the TH gene cause impaired TH activity and are associated with phenotypes ranging from autosomal recessive dopa-responsive dystonia (DRD) to progressive infantile encephalopathy. Herein, we present a patient with TH-deficiency due to two compound heterozygous missense mutations in the TH/gene, one of which is novel (p.R441P). A clinical update on TH-deficiency and clues on how to achieve a timely diagnosis of this highly treatable disorder is provided.