The molecular genetic etiology of Segawa syndrome is attributed to the impairment of tyrosine hydroxylase (TH). Most cases were affected by SNVs. The THgene encodes a rate limiting enzyme responsible for catalyzing the conversion of L-tyrosine to L-dopa in the biosynthesis pathway of dopamine, norepinephrine/epinephrine. These neurotransmitters play vital roles in maintaining the normal functioning of dopaminergic neurons and are essential for various physiological processes, including motor coordination, behavior, learning and memory, sleep mechanisms, visceral function, and hormone secretion. Deleterious mutations in the THgene directly result in dopamine deficiency and the impairment of these essential physiological processes. Also, reduced level of homovanillic acid (HVA) is used for diagnosis of Segawa syndrome.
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