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Segawa Disease (SD) was first described as ‘Hereditary Basal Ganglia Disease withmarked diurnal fluctuation’ in 1971, and in 1976, as ‘Hereditary Progressive Dystonia withmarked diurnal fluctuation (HPD)’ by Masaya Segawa. It is a childhood onset posturaldystonia responding to levodopa. Characteristic clinical features and polysomnographysuggested the pathophysiology of the disease was deficiency of the tyrosine hydroxylase(TH) of the terminal of the nigrostriatal dopamine neurons (NS-DA). The causative genewas found as the heterozygote mutation of the GTP cyclohydrolase 1 gene (GCH1) in1994. Clinically SD was classified as postural type and action type. Postural type showedstable response to levodopa through the whole course. The neuropathology of the posturaldystonia case showed decreased TH in the terminal of NS-DA neuron, but not inperikaryon, and neuron in substantia nigra was normal. The action type showed unstableresponses to levodopa. Adult onset case in action type show focal, segmental dystonia orparkinsonism. Our observations of DAT scan are normal in postural type, and abnormal inan action type case. Pathophysiology of action type was considered to be hypofuncyion ofTH in the terminal of NS-DA neuron projecting to subthalamic nucleus (STN) via D1receptor located STN, which causes impairment of STN and dysfacilitate the outputpathway of the basal ganglia.NS-DA deficiencies during development show the specific effects to the related neuronsand neuronal systems.

segawa disease