title: Monozygotic twins incompletely concordant for narcolepsy.
abstract: BACKGROUND
  Among 15 monozygotic twin pairs described in the literature, only four pairs were considered to be concordant. There is no detailed report of HLA-DRB1*1501/DQB1*0602 positive monozygotic twins concordant for narcolepsy, with marked difference in the age of onset.
  
  
  METHODS
  We compared a pair of female narcoleptic twins clinically.
  
  
  RESULTS
  Diagnosis of narcolepsy and monozygosity of the twins were confirmed. The second-born twin demonstrated a typical course of narcolepsy, whereas the first-born twin had a very late onset of recurrent daytime sleep episodes at age 45 and cataplexy at age 50 years, which was apparently triggered by chronic emotional stresses and sleep insufficiency.
  
  
  CONCLUSIONS
  The atypical course of narcolepsy in the first-born twin supports the multifactorial model for the development of narcolepsy. It was noted that cataplexy was preceded by sustained polyphasic sleep conditions. Our observation implies that the unaffected co-twins in discordant pairs could develop narcolepsy in stressful situations later in their lives.
authors.affiliation: Tokyo Metropolitan Matsuzawa Hospital (MH), Tokyo, Japan.
authors.forename: M
authors.initials: M
authors.lastname: Honda
authors.forename: Y
authors.initials: Y
authors.lastname: Honda
authors.forename: S
authors.initials: S
authors.lastname: Uchida
authors.forename: S
authors.initials: S
authors.lastname: Miyazaki
authors.forename: K
authors.initials: K
authors.lastname: Tokunaga
mesh_terms: D003577:Cytochrome P-450 Enzyme System / Q000235:genetics; D005260:Female; D020022:Genetic Predisposition to Disease; D006680:HLA Antigens / Q000235:genetics; D006801:Humans; D008875:Middle Aged; D009290:Narcolepsy / Q000175:diagnosis* / Q000209:etiology / Q000235:genetics*; D017286:Polysomnography / Q000379:methods; D012895:Sleep, REM / Q000502:physiology; D013315:Stress, Psychological / Q000523:psychology; D014430:Twins, Monozygotic / Q000235:genetics*
chemical_list: D006680:HLA Antigens; D003577:Cytochrome P-450 Enzyme System