Rett syndrome (RTT) is a neurodevelopmental disorder, which almost exclusively 
affects girls, who, after an initial period of apparently normal development, 
display gradual loss of speech and purposeful hand use, gait abnormalities and 
stereotypical hand movements. In the year 2000, mutations in the gene for the 
methyl CpG binding protein 2, MECP2, have been identified in 35-80% of the 
patients in three different studies. We have identified 15 different MECP2 
mutations in 26 of 30 Danish RTT patients. The mutations included five novel 
mutations (one point mutation, three smaller deletions involving identical 
regions in the gene, and one duplication). In contrast to the point mutations 
and the duplication, which all affect the methyl binding domain or the 
transcriptional repressing domain, the three overlapping deletions are clustered 
in the 3' end of the gene. We found no consistent correlation between the type 
of mutation and the clinical presentation of the patient or the X-inactivation 
pattern in peripheral blood. Our high mutation detection rate, compared to two 
of the previous studies, underscores the importance of the inclusion criteria of 
the patients and supports that MECP2 is the most important, if not the only, 
gene responsible for RTT.