Respiratory phenotypes are distinctly affected in mice with common Rett syndrome mutations MeCP2 T158A and R168X

- The first characterization of breathing in female mice with common Rett mutations.
- Both T158A and R168X mice exhibit abnormal hypoxic and hypercapnic responses.
- Apnea incidence, irregular breath cycle and decreased breathing rate are more severe in R168X than inT158A mice.
- Respiratory phenotypes in R168X mice are similar to those in Mecp2-null mice.
- Abnormal respiratory patterns are ameliorated with advancing age in T158A mice.

Respiratory disturbances are a primary phenotype of the neurological disorder, Rett syndrome (RTT), caused by mutations in the X-linked gene encoding methyl-CpG-binding protein 2 (MeCP2). Mouse models generated with null mutations in Mecp2 mimic respiratory abnormalities in RTT girls. Large deletions, however, are seen in only ∼10% of affected human individuals. Here we characterized respiration in heterozygous females from two mouse models that genetically mimic common RTT point mutations, a missense mutation T158A (Mecp2T158A/+) or a nonsense mutation R168X (Mecp2R168X/+). MeCP2 T158A shows decreased binding to methylated DNA, while MeCP2 R168X retains the capacity to bind methylated DNA but lacks the ability to recruit complexes required for transcriptional repression. We found that both Mecp2T158A/+ and Mecp2R168X/+ heterozygotes display augmented hypoxic ventilatory responses and depressed hypercapnic responses, compared to wild-type controls. Interestingly, the incidence of apnea was much greater in Mecp2R168X/+ heterozygotes, 189 per hour, than Mecp2T158A/+ heterozygotes, 41 per hour. These results demonstrate that different RTT mutations lead to distinct respiratory phenotypes, suggesting that characterization of the respiratory phenotype may reveal functional differences between MeCP2 mutations and provide insights into the pathophysiology of RTT.