Genetic link to poor tolerance to shift work identified

London, Nov 5 (IANS)  Some people are better able to handle constant disruptions to their daily rhythm caused by shift work than others due to certain genetic factors, a study has found.
Shift work often disrupts the circadian rhythm, which can lead to sleep disorders and daytime fatigue.
The study led by researchers at the University of Helsinki in Finland showed that a common variation in the melatonin receptor 1A (MTNR1A) gene is linked to the job-related exhaustion experienced by shift workers.
Further, it established that the risk variation of the MTNR1A gene is probably related to the methylation of DNA in the regulatory sequence of the MTNR1A gene as well as the weaker expression of the MTNR1A gene. 
The methylation of DNA is one of the epigenetic mechanisms regulating the functioning of the genome, influenced not only by variations in DNA sequence, but also environmental factors such as fluctuations in the circadian rhythm, the study said.
As it results in a smaller number of melatonin receptors, the risk variant of the gene can cause weaker natural melatonin signaling, one of the regulatory mechanisms in stabilizing the circadian rhythm.
Moreover, the influence of the risk variant of the MTNR1A gene may explain the degree to which light exposure at night disrupts the circadian rhythm of shift workers, the researchers observed. 
“The variant we have now discovered can only explain a small part of the variation between individuals, and it cannot be used as a basis to determine a person’s tolerance to shift work,” said Tiina Paunio, Professor at the University of Helsinki in Finland.
The study was published in the journal Sleep.