  Previously we have developed the concept of the dynamic pathosome, which
suggests that individual patterns of phenotype development, i.e., phenotypic
trajectories, contain more information than is commonly appreciated and that a
phenotype's past trajectory predicts its future development. In this article,
we present a pathosome-inspired approach to analyzing longitudinal data by
functional linear models. We demonstrate how to use this approach and compare
it with classical linear models on data from the Czech section of the European
Longitudinal Study of Pregnancy and Childhood (ELSPAC). Our results show that
functional linear models explain more observed variance in age at menarche from
height and weight data than the commonly used approaches. Furthermore, we
demonstrate that functional linear models can be used to identify crucial time
points that can be used to create linear models achieving almost the same
performance as functional linear models. In addition, we use data from the
Berkeley growth study (BGS) to demonstrate that growth trajectories from birth
to 15 years can be used to explain 97% of observed variance of height at 18
years, thus supporting the notion that a phenotype's past trajectory affects
its future course. Overall, this article presents experimental support for the
concept of the dynamic pathosome and presents a method that can be used as a
powerful tool for analyzing quantitative longitudinal data.
