Heritability of Sleep Homeostasis in Twins
Condition: Hereditability of Sleep Homeostasis in Twins
Study type: Observational

Summary: 
      The purpose of this study is to understand the hereditability of sleep homeostasis, i.e.,
      drive for sleep by looking at monozygotic and dizygotic twins.
    

Detailed description: 
      Excessive daytime sleepiness is a prevalent problem in our society associated with an
      increased risk of vehicular crashes and industrial accidents. Sleepiness is, in part,
      determined by fundamental biology relating to sleep homeostasis, i.e., the rate of
      accumulation of the pressure for sleep during wakefulness. A differential susceptibility to
      sleep deprivation is reported in normal subjects with large intraindividual differences in
      the degree of functional impairment produced by the same duration of sleep. Genetics are
      likely to play an important role in sleep homeostasis as shown by recent studies in inbred
      mouse strains, but whether genetics plays any role in humans and, if so, the magnitude of
      this role, is unknown. This proposal is based on the hypothesis that sleep homeostasis is a
      heritable trait in humans. Given the complexity of phenotyping to study sleep homeostasis,
      the investigators propose that studying differences in the variances of the phenotype between
      monozygotic and dizygotic twins is the optimal approach to estimate heritability of sleep
      homeostasis. The investigators will assess sleep homeostasis in 80 pairs of monozygotic and
      80 pairs of dizygotic twins by quantifying the increase in delta power during recovery sleep
      following sleep deprivation and the increase in theta power during the period of prolonged
      wakefulness. Subjects will be recruited using the PennTwins Cohort, a population-based cohort
      of about 1,800 twin pairs. If heritability of sleep homeostasis is shown, this EEG-based
      phenotyping strategy could not be easily applied to the larger scale population studies that
      will be required to assess underlying genetic variants. Thus, part of the overall strategy is
      to evaluate, and potentially validate, other approaches to phenotyping that are less
      physiologically rigorous but are more easily applied to a larger number of subjects.
      Therefore, as a subsidiary goal, the investigators will also estimate heritability of
      performance lapses during prolonged wakefulness as a surrogate method to assess sleep
      homeostasis. The investigators will particularly determine whether the differences in the
      measures based on our physiological intensive phenotypes between pairs of dizygotic twins are
      reflected in differences in this phenotyping approach that is simpler to perform. Such a
      result would indicate that this simpler method could be used in larger scale population
      studies, and will be part of future strategies to elucidate genetic variants determining
      sleepiness.
    

Observational model: Cohort
Time perspective: Prospective
Sampling method: Non-Probability Sample
Study population: 
        Subjects will be healthy MZ and DZ twins of the same gender between 18 years and 55 years
        of age.

        The investigators will not exclude any specific racial or ethnic group. African-American
        twins currently represent 3.8% of the PennTwins Cohort, i.e., 68 twin pairs. The
        investigators plan to oversample this group. The study design calls for 8 MZ and 8 DZ
        African-American twins to match the demographics of the population. There are currently no
        data that the phenotype being studied is affected by race or ethnicity.
      
Biospecimen description: 
      Blood and DNA samples will be identified by a bar-coding system. This will only be able to be
      matched to the subject ID using a secure computer database to which only the Principal
      Investigator will have access.