title: The nature of stable insomnia phenotypes.
abstract: OBJECTIVE
  We examined the 1-y stability of four insomnia symptom profiles: sleep onset insomnia; sleep maintenance insomnia; combined onset and maintenance insomnia; and neither criterion (i.e., insomnia cases that do not meet quantitative thresholds for onset or maintenance problems). Insomnia cases that exhibited the same symptom profile over a 1-y period were considered to be phenotypes, and were compared in terms of clinical and demographic characteristics.
  
  
  METHODS
  Longitudinal.
  
  
  METHODS
  Urban, community-based.
  
  
  METHODS
  Nine hundred fifty-four adults with Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition based current insomnia (46.6 ± 12.6 y; 69.4% female).
  
  
  METHODS
  None.
  
  
  RESULTS
  At baseline, participants were divided into four symptom profile groups based on quantitative criteria. Follow-up assessment 1 y later revealed that approximately 60% of participants retained the same symptom profile, and were hence judged to be phenotypes. Stability varied significantly by phenotype, such that sleep onset insomnia (SOI) was the least stable (42%), whereas combined insomnia (CI) was the most stable (69%). Baseline symptom groups (cross-sectionally defined) differed significantly across various clinical indices, including daytime impairment, depression, and anxiety. Importantly, however, a comparison of stable phenotypes (longitudinally defined) did not reveal any differences in impairment or comorbid psychopathology. Another interesting finding was that whereas all other insomnia phenotypes showed evidence of an elevated wake drive both at night and during the day, the 'neither criterion' phenotype did not; this latter phenotype exhibited significantly higher daytime sleepiness despite subthreshold onset and maintenance difficulties.
  
  
  CONCLUSIONS
  By adopting a stringent, stability-based definition, this study offers timely and important data on the longitudinal trajectory of specific insomnia phenotypes. With the exception of daytime sleepiness, few clinical differences are apparent across stable phenotypes.
authors.affiliation: Sleep Disorders and Research Center, Henry Ford Hospital, Detroit, MI.
authors.forename: Vivek
authors.initials: V
authors.lastname: Pillai
authors.affiliation: Sleep Disorders and Research Center, Henry Ford Hospital, Detroit, MI.
authors.forename: Thomas
authors.initials: T
authors.lastname: Roth
authors.affiliation: Sleep Disorders and Research Center, Henry Ford Hospital, Detroit, MI.
authors.forename: Christopher L
authors.initials: CL
authors.lastname: Drake
mesh_terms: D000328:Adult; D001007:Anxiety; D015897:Comorbidity; D003430:Cross-Sectional Studies; D003710:Demography; D003863:Depression; D039721:Diagnostic and Statistical Manual of Mental Disorders; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D008875:Middle Aged; D010641:Phenotype; D007319:Sleep Initiation and Maintenance Disorders / Q000145:classification / Q000175:diagnosis / Q000188:drug therapy / Q000503:physiopathology*; D012894:Sleep Stages / Q000502:physiology; D013997:Time Factors; D014851:Wakefulness / Q000502:physiology
keywords: insomnia; nonrestorative sleep; phenotype; prospective; sleep maintenance; sleep onset