title: Parkinson disease subtypes.
abstract: OBJECTIVE
  It is increasingly evident that Parkinson disease (PD) is not a single entity but rather a heterogeneous neurodegenerative disorder.
  
  
  OBJECTIVE
  To evaluate available evidence, based on findings from clinical, imaging, genetic and pathologic studies, supporting the differentiation of PD into subtypes.
  
  
  METHODS
  We performed a systematic review of articles cited in PubMed between 1980 and 2013 using the following search terms: Parkinson disease, parkinsonism, tremor, postural instability and gait difficulty, and Parkinson disease subtypes. The final reference list was generated on the basis of originality and relevance to the broad scope of this review.
  
  
  RESULTS
  Several subtypes, such as tremor-dominant PD and postural instability gait difficulty form of PD, have been found to cluster together. Other subtypes also have been identified, but validation by subtype-specific biomarkers is still lacking.
  
  
  CONCLUSIONS
  Several PD subtypes have been identified, but the pathogenic mechanisms underlying the observed clinicopathologic heterogeneity in PD are still not well understood. Further research into subtype-specific diagnostic and prognostic biomarkers may provide insights into mechanisms of neurodegeneration and improve epidemiologic and therapeutic clinical trial designs.
authors: Parkinson's Disease Center and Movement Disorders Clinic, Department of Neurology, Baylor College of Medicine, Houston, Texas.
authors: Mary Ann
authors: MA
authors: Thenganatt
authors: Parkinson's Disease Center and Movement Disorders Clinic, Department of Neurology, Baylor College of Medicine, Houston, Texas.
authors: Joseph
authors: J
authors: Jankovic
mesh_terms: D015415:Biomarkers / Q000737:chemistry; D006801:Humans; D009069:Movement Disorders / Q000145:classification* / Q000175:diagnosis* / Q000235:genetics; D010300:Parkinson Disease / Q000145:classification* / Q000175:diagnosis / Q000235:genetics; D014202:Tremor / Q000145:classification* / Q000175:diagnosis* / Q000235:genetics
chemical_list: D015415:Biomarkers