Synaptic functional gene group definition was based on cellular function as determined by previous protein identification and data mining for synaptic genes and gene function.11 (link) Genes were considered ‘synaptic' based on proteomic analysis of synaptic preparations.21 (link) In case of presynaptic genes, an additional expert curation was performed because only few analyses of highly purified preparations are currently available for the presynaptic proteome, except synaptic vesicles.22 (link) Hence, presynaptic genes not covered by Takamori et al.22 (link) were manually curated using published functional data and a cumulative scoring paradigm with the following set of weighted criteria: null mutation produces a synaptic phenotype; activation of the gene product (for example, receptor) or blockade thereof directly modulates synaptic function; and immunoelectron microscopy detects gene product in the synapse. More than 500 PubMed entries were manually screened. Although this approach introduces a bias toward well-studied genes, this is inherent to creating functional gene groups, as functional grouping is by definition limited to those genes for which functional data are available. Synaptic genes were subdivided into 17 functional groups based on shared cellular function (a full listing of genes assigned to functional groups is provided in the Supplementary Material, Table S4).