The expression of Na<sup>+</sup>-K<sup>+</sup>-Cl<sup>-</sup> co-transporter 1 (NKCC1), responsible for the inward transport of chlorine, is not affected, leading to a reduced KCC2/NKCC1 ratio in RTT brains.
The presence of bumetanide sensitive NKCC1 and KCC2 was analysed in cerebrospinal fluid samples from a control pediatric population (1 day to 14 years of life) and from Rett syndrome patients (2 to 19 years of life), by immunoblot analysis.