title: Spinocerebellar ataxia in monozygotic twins.
abstract: BACKGROUND
  Although phenotypic heterogeneity in autosomal dominant spinocerebellar ataxia (SCA) has been explained in part by genotypic heterogeneity, clinical observations suggest the influence of additional factors.
  
  
  OBJECTIVE
  To demonstrate, quantitate, and localize physiologic abnormalities attributable to nongenetic factors in the development of hereditary SCA.
  
  
  METHODS
  Quantitative assessments of ocular motor function and postural control in 2 sets of identical twins, one with SCA type 2 and the other with episodic ataxia type 2.
  
  
  METHODS
  University laboratory.
  
  
  METHODS
  Saccadic velocity and amplitude, pursuit gain, and dynamic posturography.
  
  
  RESULTS
  We found significant differences in saccade velocity, saccade metrics, and postural stability between each monozygotic twin. The differences point to differential involvement between twins of discrete regions in the cerebellum and brainstem.
  
  
  CONCLUSIONS
  These results demonstrate the presence of quantitative differences in the severity, rate of progression, and regional central nervous system involvement in monozygotic twins with SCA that must be owing to the existence of nongermline or external factors.
authors.affiliation: Department of Otolaryngology, Graduate Program in Neuroscience, University of Minnesota, Minneapolis 55455, USA.
authors.forename: John H
authors.initials: JH
authors.lastname: Anderson
authors.forename: Peka S
authors.initials: PS
authors.lastname: Christova
authors.forename: Ting-dong
authors.initials: TD
authors.lastname: Xie
authors.forename: Kelly S
authors.initials: KS
authors.lastname: Schott
authors.forename: Kenneth
authors.initials: K
authors.lastname: Ward
authors.forename: Christopher M
authors.initials: CM
authors.lastname: Gomez
mesh_terms: D000328:Adult; D000368:Aged; D001933:Brain Stem / Q000503:physiopathology; D002531:Cerebellum / Q000503:physiopathology; D004200:Diseases in Twins / Q000235:genetics*; D005260:Female; D006801:Humans; D008297:Male; D011187:Posture / Q000502:physiology; D012438:Saccades / Q000502:physiology; D020754:Spinocerebellar Ataxias / Q000235:genetics* / Q000503:physiopathology*; D014430:Twins, Monozygotic / Q000235:genetics* / Q000706:statistics & numerical data