Tyrosine hydroxylase (TH) deficiency is a rare autosomal recessive inborn error of dopamine transmission, which the deficient gene is at the chromosome 11, also called'Segawa Syndrome'.
Recessively inherited deficiency of TH was recently identified and incorporated into recent concepts of genetic dystonias as the cause of recessive Dopa-responsive dystonia or Segawa's syndrome in analogy to dominantly inherited GTP cyclohydrolase I deficiency.
In the AR-DRD with Segawa's syndrome, a point mutation in TH (Gln381Lys) resulted in a pronounced decrease in TH activity to about 15% of that of the wild type.