A decreased expression of mGlu2 and mGlu3 receptors has been observed in a mouse model and in patients with Rett syndrome, whereas an increased expression of both mGlu2 and mGlu3 receptors has been reported in a mouse model of MECP2 duplication syndrome (Vermudez et al. 2022). The gene discussed is MECP2; the disease is atypical Rett syndrome.