Genetic and Behavioral Variation Underlying an Integrated Temporal Phenotype in an Admixed South American Population

Chronotype, a trait influenced by genetics and behavior, impacts how individuals organize their daily rest and activity patterns. In Uruguay, individuals with roots from African, European, and Indigenous ancestries tend to exhibit eveningness. However, the genetic basis of this trait in this population has not been explored. A study analyzed young healthy adults from the chronotype extremes, combining self-reports, actigraphy data, and whole-genome sequencing.

The participants were predominantly of European descent, with smaller contributions from Indigenous and African ancestry. The most genetically variable region was PER2, a gene linked to late chronotypes. Individuals carrying the T-allele of a specific PER2 variant (rs35333999) showed differences in their peak activity times compared to non-carriers.

By examining genetic clusters, researchers found that certain variants were more common in early or late chronotypes. Further analysis revealed that these genetic differences were primarily found in genes involved in breaking down the circadian regulatory system, particularly BTRC, a protein linked to PER2 degradation. The study also uncovered a joint behavioral component, including food intake, exercise, light exposure, and sleep timing, which correlated with the timing of the body's internal clock (dim-light melatonin onset).

This suggests a complex relationship between genetic factors and behavioral patterns in shaping an individual's chronotype.