State-of-the-art therapies for Rett syndrome

Abstract

Rett syndrome (RTT) is an X-linked neurogenetic disorder caused by mutations of the MECP2 (methyl-CpG-binding protein 2) gene. Over two decades of work established MeCP2 as a protein with pivotal roles in the regulation of the epigenome, neuronal physiology, synaptic maintenance, and behaviour. Given the genetic aetiology of RTT and the proof of concept of its reversal in a mouse model, considerable efforts have been made to design therapeutic approaches to re-express MeCP2. By being at the forefront of the development of innovative gene therapies, research on RTT is of paramount importance for the treatment of monogenic neurological diseases. Here we discuss the recent advances and challenges of promising genetic strategies for the treatment of RTT including gene replacement therapies, gene/RNA editing strategies, and reactivation of the silenced X chromosome. WHAT THIS PAPER ADDS: Recent advances shed light on the promises of gene replacement therapy with new vectors designed to control the levels of MeCP2 expression. New developments in DNA/RNA editing approaches or reactivation of the silenced X chromosome open the possibility to re-express the native MeCP2 locus at endogenous levels. Current strategies still face limitations in transduction efficiency and future work is needed to improve brain delivery.

FIGURE 1

Innovative therapeutic developments in Rett syndrome. (a) DNA editing. Double‐strand breaks guided by Cas9 and its guide RNA can be repaired by non‐homologous end joining (NHEJ) or by homology‐directed repair (HDR) in the presence of donor DNA. (b) RNA editing. A modified Cas13 fused to adenosine deaminase acting on RNA (ADAR) which deaminates an adenosine to an inosine at a specific target site. The inosine is then read as a guanine by the translation machinery. (c) X‐chromosome reactivation. In female cells, one of the two X chromosomes is randomly inactivated to balance the expression of genes. Pharmacological strategies allow the reactivation of the inactive X (Xi) carrying the healthy Mecp2 gene.