Segawa Syndrome (Dopa-Responsive Dystonia): Current Concepts in Pathogenesis, Clinical Spectrum, Diagnosis, and Contemporary Management
Segawa Syndrome (Dopa-Responsive Dystonia): Current Concepts in Pathogenesis, Clinical Spectrum, Diagnosis, and Contemporary Management
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Original abstract
Segawa syndrome, also known as dopa-responsive dystonia (DRD), is a rare inherited neurometabolic movement disorder characterized by childhood-onset dystonia, gait abnormalities, marked diurnal fluctuation, and dramatic responsiveness to low-dose levodopa therapy. [1,2] Since its original description by Segawa and colleagues in 1976, substantial advances have occurred in the understanding of the molecular genetics, neurotransmitter biochemistry, clinical heterogeneity, and therapeutic responsiveness of this disorder. [1,3] Classical Segawa syndrome is most commonly associated with autosomal dominant mutations involving the guanosine triphosphate cyclohydrolase I (GCH1) gene, resulting in impaired tetrahydrobiopterin (BH4) synthesis and subsequent dopamine deficiency within the nigrostriatal pathway. [3,4] Additional pathogenic variants involving TH, SPR, and related neurotransmitter biosynthetic pathways have expanded the phenotypic spectrum to include atypical and complex forms associated with parkinsonism, developmental delay, autonomic dysfunction, psychiatric manifestations, and cognitive impairment. [5,11] The disorder frequently presents diagnostic challenges because of significant phenotypic overlap with cerebral palsy, hereditary spastic paraplegia, juvenile Parkinson disease, idiopathic dystonia, and neurodegenerative disorders. [6,10,21] Delayed diagnosis remains common despite the existence of highly effective treatment, resulting in avoidable disability, skeletal deformities, psychosocial impairment, and reduced quality of life. [18,21] The hallmark clinical feature remains a dramatic and sustained response to levodopa therapy, which distinguishes DRD from most progressive neurodegenerative movement disorders. [8] Recent advances in molecular diagnostics, next-generation sequencing, cerebrospinal fluid neurotransmitter analysis, and functional neuroimaging have improved disease recognition and expanded understanding of genotype–phenotype correlations. [5,10,11] Nevertheless, contemporary controversies persist regarding diagnostic classification, atypical phenotypes, long-term disease progression, neuropsychiatric involvement, and optimization of individualized therapeutic strategies. [17,22] This comprehensive descriptive review examines the epidemiology, molecular pathogenesis, neurochemical mechanisms, clinical presentation, diagnostic evaluation, differential diagnosis, treatment approaches, prognosis, contemporary controversies, limitations of current evidence, and future research directions related to Segawa syndrome.