The finding with NR1 is important, because this receptor seems to be modulated by activity, and we know that MeCP2 level increases in neurons throughout childhood-implying a link to neuronal activity," said Zoghbi. Thus, she said, the gradual onset of Rett syndrome symptoms in children, who begin developing normally as infants, might be explained by the progressive pathology caused by abnormalities in proteins such as NR1. Using the mouse model of Rett syndrome, the researchers next searched for splicing alterations in genes that were active in the cerebral cortex. For this experiment, they used a microarray of thousands of such genes supplied by co-author Jason Johnson of Merck. The researchers found that splicing was altered in a significant number of genes from the mutant mice as compared to normal mice. "So, we now know that in this mouse model of Rett syndrome, there is quite a bit of RNA splicing alteration in the brain," said Zoghbi. "The next big question is exactly how these splicing alterations relate to changes in gene expression that might occur in this syndrome