<prompt> Answer this question truthfullyCould you provide me with the original sentence or context in order to confirm the necessary changes?  <response>: <reason> Males with pathogenic MECP2 mutations usually die within the first 2 years from severe encephalopathy, unless they have an extra X chromosome often described as Klinefelter syndrome, or have somatic mosaicism.Females can live up to 40 years or more. Laboratory studies on Rett syndrome may show abnormalities such as:EEG abnormalities from 2 years of age atypical brain glycolipids elevated CSF levels of beta-endorphins and glutamate reduction of substance P decreased levels of CSF nerve growth factorsA high proportion of deaths are abrupt, but most have no identifiable cause; in some instances death is the result most likely of:spontaneous brainstem dysfunction cardiac arrest seizures cardiac conduction abnormalities - abnormally prolonged QT interval on ECG gastric perforation 