Rett syndrome (RTT) is a progressive neurodevelopmental disorder that is caused 
by mutations in the X-linked methyl-CpG-binding protein2 (MECP2) gene. In this 
study, the MECP2 sequences in 121 unrelated Chinese patients with classical or 
atypical RTT were screened for deletions and mutations. In all, we identified 45 
different MECP2 mutations in 102 of these RTT patients. The p. T158M mutation 
(15.7%) was the most common, followed in order of frequency by p. R168X (11.8%), 
p. R133C (6.9%), p. R270X (6.9%), p. G269fs (6.9%), p. R255X (4.9%), and p. 
R306C (3.9%). In addition, we identified five novel MECP2 mutations: three 
missense (p. K305E, p. V122M, p. A358T), one insertion (c.45-46insGGAGGA), and 
one 22 bp deletion (c.881-902del22). Large deletions represented 10.5% of all 
identified MECP2 mutations. Conversely, mutations in exon 1 appeared to be rare 
(0.9%). The remaining cases without MECP2 mutations were screened for the 
cyclin-dependent kinase-like 5 (CDKL5) gene using denaturing high-performance 
liquid chromatography (DHPLC). One synonymous mutation (p. I72I) was found in 
exon 5, suggesting that CDKL5 is a rare cause of RTT. The overall MECP2 mutation 
detection rate for this patient series was 84.3:87.9% in 107 classical RTT cases 
and 57.1% in 14 atypical RTT cases. Moreover, there were two patients with 
homozygous mutations and normal female karyotypes. However, we did not pinpoint 
a significant relationship between genotype and phenotype in these cases.