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RAI1 Overexpression Promotes Disruption of Central Circadian Components and Dyssomnia in Potocki-Lupski Syndrome

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Retinoic acid-induced 1 (RAI1) encodes a dosage-sensitive gene that when haploinsufficient results in Smith-Magenis syndrome (SMS) and when overexpressed results in Potocki-Lupski syndrome (PTLS).  Phenotypic and molecular evidence illustrates that haploinsufficiency of RAI1 disrupts circadian rhythm through the dysregulation of the master circadian regulator, CLOCK, and other core circadian components, contributing to prominent sleep disturbances in SMS.  However, the phenotypic and molecular characterization of sleep features in PTLS have not been elucidated.  Utilizing the Pittsburgh Sleep Quality Index (PSQI), caregivers of 15 school-age children with PTLS reported difficulties in initiating sleep.  Indeed, over 70% of individuals manifested moderate to severe sleep latency, as defined by the PSQI.  Moreover, these individuals manifested difficulties in sleep maintenance, with middle of the night and early morning awakenings.  When assessing daytime sleepiness via the Epworth Sleepiness Scale, only ~21% of the individuals manifested excessive daytime somnolence.  This indicates that mild dyssomnia characterizes the majority of the sleep phenotype, with occasionally problematic daytime somnolence, a phenotype different than that expressed by individuals with SMS, where daytime sleepiness is a chronic problem.  Gene expression analysis of the core circadian machinery in the hypothalamus of the PTLS mouse model (Rai1-Tg) found significant dysregulation of the transcriptional activators, Clock and Arntl, and the transcriptional repressors, Per1-3 and Cry1/2, during both light and dark phases.  These findings suggest a partial loss of circadian entrainment typically evoked by environmental photic cues.  Examination of circadian clock gene expression in the Rai1-Tg mouse heart, liver, and kidney found unchanged expression of Clock and most of its downstream targets during both light and dark phases, suggesting an asynchronized circadian rhythm.  Further, examination of circadian gene expression in synchronized PTLS lymphoblasts revealed reduced transcripts of the Period (PER1-3) family and normal expression of CRY1/2.  The finding that central circadian gene expression was altered while many peripheral circadian components were intact suggests a tissue-specific circadian uncoupling of the circadian machinery due to Rai1 overexpression.  Overall, our results demonstrate that overexpression of RAI1 results in sleep deficiencies in individuals with PTLS due to a lack of properly regulated circadian machinery gene expression and highlight the importance of evaluating sleep concerns in individuals with PTLS.

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