TH and hyperinsulinemic hypoglycemia, familial, 4: In the case of TH deficiency, based on the severity of symptoms and responsiveness to levodopa, the clinical phenotypes are classified into TH-deficient DRD (mild form), TH-deficient infantile parkinsonism with motor delay (severe form), and TH-deficient progressive infantile encephalopathy (very severe form)16, 17).