Microarray experimental design. Four sets of six microarray experiments were conducted. The double arrows represent co-hybridization of the samples at each end of the arrows. Six individual RTT frontal cortices were co-hybridized with six individual control frontal cortices. For example, the frontal cortex of patient RTT1 was compared with the occipital cortex of RTT1. Additionally, where the frontal cortex of a RTT sample was compared to the frontal cortex of a control sample, the comparison between the occipital cortices was conducted between the same samples. For example RTT1 frontal cortex vs. Con4 frontal cortex, RTT1 occipital cortex vs. Con4 occipital cortex. Each experiment was repeated and the fluorescent cyanine dyes were reversed.