Period3 gene in disorder of consciousness: The role of neuroimaging in understanding the relationship between genotype and sleep. A brief communication

Background Several methodologies including neuroimaging and sleep evaluation are being developed to complement the clinical bedside examinations in patients with disorder of consciousness (DOC). Recently, we demonstrated a possible association between Period3 (Per3) variable number tandem repeat (VNTR) polymorphism and functional impairment of DOC patients, speculating a possible role of this gene in sleep regulation. Aim To assess whether the degree of structural and metabolic damage of the main brain areas involved in the sleep generation and homeostasis may influence the different outcome of DOC patients carrying the Per35/5 genotype in comparison to Per34/4 ones. Methods For the present study, we reviewed 44 DOC patients from the Coma Research Centre of the Fondazione IRCCS Istituto Neurologico “C. Besta” of Milan. All patients underwent to polysomnographic sleep evaluation, cerebral structural magnetic resonance imaging (MRI) and 18F–fluoro-2-deoxyglucose positron emission tomography (FDG-PET) analysis. Results Our DOC patients presented a moderate anatomical (median score 2) and metabolic damage (median value 2.36 SUVmean) of the sleep areas at both MRI and FDG-PET evaluation. Total sleep time seemed to be higher in 5/5 genotype DOC patients (median value Per35/5, 221 min, range 126–323 min; median value Per34/4, 167 min, range 36–477 min; and median value Per34/5, 187 min, range 29–422 min). However, the MRI scores and FDG-PET values of whole brain, overall sleep areas, hypothalamus, midbrain and thalamus did not differ by genotype distribution. Conclusion Although limited by the small sample size, our data might support the idea that Per3 genetic predisposition in DOC patients could affect impairment and residual cognitive functions through sleep homeostasis independently from structural and/or metabolic integrity of sleep areas.