The gene expression profile of the brain is clearly distinct from other tissues, as shown by a comparison of global expression patterns across 45 different human tissues, including the CNS; in this comparison, many genes have been identified that distinguish the CNS from all other tissues (Roth, et al., 2006). Several computational analyses of gene expression variability across different human tissues using exon array (de la Grange, Gratadou, Delord, Dutertre, & Auboeuf, 2010) and RNA-Seq (Ramskold, Wang, Burge, & Sandberg, 2009) data suggest that the brain (together with the kidney and testes) has higher gene expression levels and transcriptome complexity compared to other tissues. That is, brain tissue has a high number of expressed genes – 13,298 genes were found to be expressed in the human brain (the range of the number of genes expressed across different human tissues is from 11,199 to 15,518), and the brain transcriptome has more diverse populations of RNA (de la Grange, Gratadou, Delord, Dutertre, & Auboeuf, 2010; Ramskold, Wang, Burge, & Sandberg, 2009) than other tissues and cell types. There is evidence that the
