Fragile X Spectrum as Model for Neurogenetic Mechanisms of Cognitive Dysfunction

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Fragile X is unique among neurogenetic conditions because it is the only such disorder with a dose-response mechanism based on a single gene (CGG-repeat-dependence of phenotypes). Also, it produces varying outcomes as a result of different pathogenic mechanisms related to FMR1 gene dysregulation - low/absent FMR1 protein (FMRP) in fragile X syndrome; elevated levels of "toxic" FMR1 RNA. As a result of these characteristics, fragile X provides a unique model for developing a "molecules to mind" explanation of a neurogenetic disorder that can then be used to generate hypotheses about the genetic bases of disorders with less clear molecular mechanisms. Thus, the overall objective of this component is to understand how variations in the mutation of a single gene (FMR1) produce a spectrum of cognitive dysfunction in both childhood and adulthood. To this end, we will generate the first detailed neurocognitive profile of an integrated set of cognitive domains that preliminary data suggest are highly vulnerable to changes in the expression of FMRP. The profile will consist of data derived from hypothesis-driven experimental cognitive processing tasks and magnetic resonance imaging (MRI) methods that will produce structural, functional and connectivity measures. We will refer to this profile as the FMR1 Sensitive Neurocognitive Profile (FSNP). It will focus on spatiotemporal, memory, numerical, and executive cognitive functions. It will be characterized in children and adults who have the fragile X full mutation and extended to smaller alleles in the premutation range, and to unaffected (normal repeat) controls. In our investigations we will consider the effect of two continuous variables: FMRP expression level and FMR1 mRNA level, and one categorical variable: phase of development (childhood or adulthood). There will be extensive interaction with other components. With Project 1 we will share the neurocognitive specification of phenotypes that will foster understanding of molecular mechanisms and treatment effects and we will be dependent on their molecular and cellular assessments. With Project 2 there will be a bidirectional feed of behavioral and MRI assessments, especially to drive investigations of the "mixed phenotype" where FMRP and FMR1 RNA changes may interact. Data (and methods) shared between Projects 3 and 4 will extend lifespan analyses, clarify neurochemical mechanisms and neural progressions toward FXTAS, and drive novel MRI analysis method development.