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Deficient K<jats:sup>+<\/jats:sup>-Cl<jats:sup>\u2014<\/jats:sup>co-transporter 2 (<jats:italic>KCC2<\/jats:italic>) expression is suggested to play a key role in the neurodevelopmental delay in RTT patients\u2019 neuronal networks. KCC2 is a major player in neuronal maturation by supporting the GABAergic switch, through the regulation of neuronal chlorine homeostasis. Previous studies suggest that MeCP2 mutations lead to changed <jats:italic>KCC2<\/jats:italic> expression levels, thereby causing a disturbance in excitation\/inhibition (E\/I) balance. To investigate this, we performed protein and RNA expression analysis on post mortem brain tissue from RTT patients and healthy controls. We showed that <jats:italic>KCC2<\/jats:italic> expression, in particular the <jats:italic>KCC2a<\/jats:italic> isoform, is relatively decreased in RTT patients. The expression of Na<jats:sup>+<\/jats:sup>-K<jats:sup>+<\/jats:sup>-Cl<jats:sup>\u2212<\/jats:sup> co-transporter 1 (<jats:italic>NKCC1<\/jats:italic>), responsible for the inward transport of chlorine, is not affected, leading to a reduced <jats:italic>KCC2<\/jats:italic>\/<jats:italic>NKCC1<\/jats:italic> ratio in RTT brains. Our report confirms <jats:italic>KCC2<\/jats:italic> expression alterations in RTT patients in human brain tissue, which is in line with other studies, suggesting affected E\/I balance could underlie neurodevelopmental defects in RTT patients.<\/jats:p>","DOI":"10.1186\/s40478-019-0852-x","type":"journal-article","created":{"date-parts":[[2019,12,3]],"date-time":"2019-12-03T11:04:01Z","timestamp":1575371041000},"update-policy":"https:\/\/doi.org\/10.1007\/springer_crossmark_policy","source":"Crossref","is-referenced-by-count":48,"title":["KCC2 expression levels are reduced in post mortem brain tissue of Rett syndrome patients"],"prefix":"10.1186","volume":"7","author":[{"given":"Lisa","family":"Hinz","sequence":"first","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Joan","family":"Torrella Barrufet","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-4416-3875","authenticated-orcid":false,"given":"Vivi M.","family":"Heine","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"297","published-online":{"date-parts":[[2019,12,3]]},"reference":[{"key":"852_CR1","doi-asserted-by":"publisher","first-page":"223","DOI":"10.1113\/JP270966","volume":"594","author":"AP Abdala","year":"2016","unstructured":"Abdala AP, Toward MA, Dutschmann M, Bissonnette JM, Paton JFR (2016) Deficiency of GABAergic synaptic inhibition in the K\u00f6lliker-Fuse area underlies respiratory dysrhythmia in a mouse model of Rett syndrome. 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