Tyrosine hydroxylase (TH) is a crucial enzyme catalyzing the first committed step in catecholamine biosynthesis, converting tyrosine to L-DOPA, a precursor for dopamine, norepinephrine, and epinephrine production. TH is predominantly expressed in dopaminergic and noradrenergic neurons throughout the central and peripheral nervous systems, with localization to cytoplasmic compartments, synaptic vesicles, and the plasma membrane. The enzyme's activity is essential for midbrain dopamine neuron (mDAN) function and survival 1. Loss or dysfunction of TH-positive dopaminergic neurons is pathologically relevant to Parkinson's disease, where dopamine depletion causes progressive motor dysfunction 1. Segawa syndrome, an autosomal recessive neurological disorder, results from TH mutations causing severe reduction in dopamine and catecholamine synthesis, leading to early-onset dystonia, hypokinesia, and diurnal motor fluctuations. Beyond dopaminergic functions, TH participates in regulating cardiovascular function, stress responses, and neuroendocrine signaling. Recent evidence from cell transplantation studies demonstrates that TH expression marks functional dopaminergic grafts, with poor survival of TH+ neurons in initial transplantation contexts but improved outcomes when combined with immunomodulatory strategies 1. These findings establish TH as a critical molecular marker and functional determinant of dopaminergic neuron identity with direct implications for neurodegenerative disease pathogenesis and regenerative therapeutic approaches.