Males with pathogenic MECP2 mutations usually die within the first 2 years from severe encephalopathy, unless they have one or more extra X chromosomes, or have somatic mosaicism. Male fetuses with the disorder rarely survive to term. Because the disease-causing gene is located on the X chromosome, a female born with an MECP2 mutation on her X chromosome has another X chromosome with an ostensibly normal copy of the same gene, while a male with the mutation on his X chromosome has no other X chromosome, only a Y chromosome; thus, he has no normal gene. Without a normal gene to provide normal proteins in addition to the abnormal proteins caused by a MECP2 mutation, the XY karyotype male fetus is unable to slow the development of the disease, hence the failure of many male fetuses with a MECP2 mutation to survive to term. Females with a MECP2 mutation, however, have a non-mutant chromosome that provides them enough normal protein to survive longer. Research shows that males with<unk>  may result from Klinefelter's syndrome, in which the male has an XXY karyotype. Thus, a non-mutant MECP2 gene is necessary for a<unk> 's-affected embryo to survive in most cases, and the embryo, male or female, must have another X chromosome. There have, however, been several cases of 46,XY karyotype males with a MECP2 mutation (associated with classical<unk>  in females) carried to term, who were affected by neonatal encephalopathy and died before 2 years of age. The incidence of<unk>  in males is unknown, partly owing to the low survival of male fetuses with the<unk> -associated MECP2 mutations, and partly to differences between signs caused by MECP2 mutations and those caused by<unk> 's. Females can live up to 40 years or more. Laboratory studies on<unk>  may show abnormalities such as: * EEG abnormalities from 2 years of age * atypical brain glycolipids * elevated CSF levels of beta-endorphin and glutamate * reduction of substance P * decreased levels of CSF nerve growth factors A 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, likely due to long QT syndrome, ventricular tachycardia or other arrhythmias * seizures * gastric perforation
Rett syndrome
1p36 deletion syndrome
Fragile X syndrome
Angelman syndrome
Poland syndrome
Childhood disintegrative disorder
Fragile X-associated tremor/ataxia syndrome
Snyder–Robinson syndrome