Most cases of Rett syndrome (RS) are associated with mutations in the coding region of MeCP2, which are partially correlated with the variable RS phenotype. The goal of this Project is to provide a better understanding of RS phenotypical variability by characterizing, in a continuum from MeCP2 levels to histone acetylation, molecular profiles of major MeCP2 mutations in RS. These studies, which will be primarily conducted in brain samples from RS subjects with and without MeCP2 mutations, will be extended to lymphocytes from the RS subjects proposed in Project 1 in order to both develop prototypic "RS molecular profiles" and for molecular-phenotypical correlations. To gain additional insight into the neurobiology of MeCP2 mutations, this Project will also delineate molecular profiles of olfactory neurons from RS patients and of tissues and cultured cells from the mouse models relevant to RS proposed in Project 5. Specifically, Aim 1 will characterize patterns (i.e., levels and compartmentalization) of MeCP2 expression in the samples mentioned above, while Aim 2 will delineate the consequences of MeCP2 mutations on levels of other methyl-binding proteins and transcriptional regulators (Aim 2a) and on patterns of histone acetylation (Aim 2b) in the same samples. Finally, the exploratory Aim 3 will conduct a preliminary identification of proteins associated with MeCP2 in control and RS cells, by initially transfecting cells with normal and "mutated" MeCP2 constructs and then by directly assessing lymphoblasts from patients with selected or no MeCP2 mutations. We hypothesize that different MeCP2 mutations will show distinct cell population-dependent patterns of MeCP2 expression, and that these abnormal MeCP2 patterns are associated with changes in other transcriptional regulators and in histone acetylation which can contribute to phenotypical variability and severity in RS. Data to be obtained in this and the other projects will lend support to the general hypothesis of this PPG, that variability in the neurologic phenotype of RS is the result of the differential effect of distinct MeCP2 mutations upon differentiation and function of specific neuronal populations and their connections.