Seventy-one sporadic and 7 familial Rett syndrome (RTT) patients were screened for MECP2 mutations by direct sequencing and the pattern of X chromosome inactivation (XCI) was determined in 39 RTT patients at the Baylor College of Medicine, Houston, TX. Twenty-three different disease-causing MECP2 mutations were identified in 54 of 71 (76%) sporadic and in 2 of 7 (29%) familial cases. Thirty-one of 34 patients (91%) with classic RTT had random XCI. Nonrandom XCI was associated with milder phenotypes. RTT is caused by a partial loss of MeCP2 function. 
COMMENT. Different MECP2 mutations have similar Rett syndrome phenotypic consequences, and random X chromosome inactivation plays a role in the full phenotypic spectrum of classic RTT.
Amino acid receptors in frontal cortex in RTT syndrome. A study at Johns Hopkins University, Kennedy Krieger Institute, showed that the densities of N-methyl-D-aspartate, AMPA, and GABA, measured autoradiographically in the superior frontal gyrus, were higher in younger patients and lower in older patients when compared with controls. The age-related changes in amino acid receptor density could be correlated with the stages of RTT syndrome, younger age-stage II/III regression and seizures to a less epileptic plateau stage in older girls.