Baird, A.L. and Coogan, Andrew and Siddiqui, A. and Donev, R.M. and Thome, J.
Adult attention-deficit hyperactivity disorder is associated
with alterations in circadian rhythms at the behavioural,
endocrine and molecular levels.
Attention-deficit hyperactivity disorder (ADHD) in adults is associated with impaired sleep, and
it has been postulated that this impairment may contribute to the psychopathology of this
common condition. One key driver of sleep/wake cycles is the circadian system, which at the
molecular level consists of a series of transcriptional feedback loops of clock genes, which in
turn produce endocrine, physiological and behavioural outputs with a near 24 h periodicity.
We set out to examine circadian rhythms at the behavioural, endocrine and molecular levels
in ADHD. Adults with ADHD as well as age- and sex-matched controls were recruited.
Circadian rhythms were measured by means of actigraphy for the determination of gross
motor patterns, by self-sampling of oral mucosa for assessment of rhythmic expression of the
clock genes BMAL1 and PER2, and by estimation of salivary cortisol and melatonin levels.
Actigraphic analysis revealed significant diurnal and nocturnal hyperactivity in the ADHD
group, as well as a significant shorter period of best fit for the locomotor circadian rhythm in
ADHD. BMAL1 and PER2 showed circadian rhythmicity in controls with this being lost in the
ADHD group. Cortisol rhythms were significantly phase delayed in the ADHD group. These
findings indicate that adult ADHD is accompanied by significant changes in the circadian
system, which in turn may lead to decreased sleep duration and quality in the condition.
Further, modulation of circadian rhythms may represent a novel therapeutic avenue in the
management of ADHD.
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