better than the base model and comparable to KL grade (Table 1, Figure1). Finally, all the results consistently improved when a regularized model was applied. Applying regularized logistic regression developed in a machine learning fashion, showed excellent predictive performance of the US features for all models in which these were included (Table 1). Conclusions: Baseline US features could predict future TKR cases comparably well as conventional plain radiography, scored with KL grading, and better than the base model which included clinical covariates only. Finally, the predictive performance of all the built models was improved when a regularized model was used for prediction.

Monozygotic (MZ) twins subjected to different environmental exposures offer an informative, naturally occurring, co-twin control design. Given their genetic identity, differences in physical, medical and behavioral outcomes between them can be associated with their experiential differences. In space research, a wide range of ethological studies has been conducted on the effects of microgravity on sensorimotor activity and on social group behavior during orbital flights, in a large array of isolated and confined environments and for short-term, mid-term and long-term missions. The study of MZ twin astronaut, Scott Kelly (SK), who spent nearly one-year at the International Space Station (ISS) while his co-twin, Mark Kelly, stayed on earth, is a unique opportunity to identify factors affecting astronauts' health and the extent to which a space mission modifies different adaptive systems at the genetic and epigenetic levels.