Developmental trajectories in genetic disorders

Abstract As the cognitive system develops over infancy and through childhood, profound changes in capacity and complexity occur. It is no surprise, then, that neurodevelopmental disorders of genetic origin are emergent over time. Characteristic cognitive profiles arise as neurodevelopmental constraints and multiple genetic and environmental factors influence an interactive network of developing systems. In order to construct a mechanistic understanding of this developmental process (both in the typically developing system and in those with additional, atypical constraints) it is necessary to take a developmental perspective. In this paper, we argue that a developmental trajectories approach is the most suitable framework within which to understand the highly complex, dynamic system that is the developing brain. The trajectories approach involves constructing algebraic functions linking performance on two measures, allowing a comparison of developmental change across typically and atypically developing groups. We advocate the use of brain measures to complement and extend our understanding of behaviorally measured cognitive change, on the basis that cognitive development is shaped by brain structure and function. We explore possible patterns of interaction between brain and behavioral trajectories, and give empirical examples of using the trajectories method with neurodevelopmental disorders of genetic origin. We conclude that this approach can offer a window onto how subtle neurocognitive anomalies in infancy can develop into the characteristic cognitive profiles seen in childhood and beyond, in those individuals with genetically determined developmental disorders.