To further demonstrate the effects of optimal codon content on stability using endogenously-occurring human mRNA coding sequences, we designed an additional set of variable optimality reporters for an mRNA of similar overall length, MECP2. This gene is an attractive candidate for potential titration of gene expression at the level of mRNA decay, as both loss- and gain-of-function mutations in MECP2 manifest as Rett syndrome and MECP2 duplication syndrome, respectively [51,52]. This evidence concerns the gene MECP2 and atypical Rett syndrome.