TH and tyrosine hydroxylase deficiency: There have been described three phenotypes: (1) TH-deficient dopa-responsive dystonia (the mild form of TH deficiency) age onset: 12 months to 12 years of age, initial symptoms are typically lower-limb dystonia and/or difficulty in walking (2) TH-deficient infantile HRS (hypokinesia, rigidity of extremities, and/or tremor) with motor delay (the severe form), age at onset: 3 to 12 months, and (3) TH-deficient progressive infantile encephalopathy (the very severe form), age at onset: 3 to 6 months: severe hypokinesia and limb hypertonia