The location of the gene responsible for<unk>  Genetically,<unk>  <unk>  is caused by mutations in the gene MECP2 located on the X chromosome (which is involved in transcriptional silencing and epigenetic regulation of methylated DNA), and can arise sporadically or from germline mutations. In less than 10% of<unk>  cases, mutations in the genes CDKL5 or FOXG1 have also been found to resemble it.<unk>  is initially diagnosed by clinical observation, but the diagnosis is definitive when there is a genetic defect in the MECP2 gene. It has been argued that<unk>  is in fact a neurodevelopmental condition as opposed to a neurodegenerative condition. One piece of evidence for this is that mice with induced<unk>  show no neuronal death, and some studies have suggested that their phenotypes can be partially rescued by adding functional MECP2 gene back when they are adults. This information has also helped lead to further studies aiming to treat the disorder. Sporadic mutations In at least 95% of<unk>  cases, the cause is a de novo mutation in the child. That is, it is not inherited from either parent. Parents are generally genotypically normal, without a MECP2 mutation. In cases of the sporadic form of<unk> , the mutated MECP2 is thought to derive almost exclusively from a de novo mutation on the male copy of the X chromosome. It is not yet known what causes the sperm to mutate, and such mutations are rare. Germline mutations It can also be inherited from phenotypically normal mothers who have a germline mutation in the gene encoding methyl-CpG-binding protein-2, MeCP2. In these cases, inheritance follows an X-linked dominant pattern and is seen almost exclusively in females, as most males die in utero or shortly after birth. MECP2 is found near the end of the long arm of the X chromosome at Xq28. An atypical form of<unk> , characterized by infantile spasms or early onset epilepsy, can also be caused by a mutation to the gene encoding cyclin-dependent kinase-like 5 (CDKL5). As stated by Aine Merwick, Margaret O'Brien, and Norman Delanty in an article on gene disorders titled Complex single gene disorders and epilepsy,<unk>  affects one in every 12,500 female live births by age 12 years."
Rett syndrome
1p36 deletion syndrome
Fragile X syndrome
Angelman syndrome
Poland syndrome
Childhood disintegrative disorder
Fragile X-associated tremor/ataxia syndrome
Snyder–Robinson syndrome