Epigenetic mechanisms have been proposed to play a role in the etiology of
autism. This hypothesis is supported by the discovery of increased MECP2 promoter methylation associated with decreased
MeCP2 protein expression in
autism male brain. To further understand the influence of female X chromosome inactivation (XCI) and neighboring methylation patterns on aberrant MECP2 promoter methylation in
autism, multiple methylation analyses were peformed on brain and blood samples from individuals with
autism.
Bisulfite sequencing analyses of a region 0.6 kb upstream of MECP2 in brain
DNA samples revealed an abrupt transition from a highly methylated region in both sexes to a region unmethylated in males and subject to XCI in females.
Chromatin immunoprecipitation analysis demonstrated that the CCTC-binding factor (CTCF) bound to this transition region in neuronal cells, consistent with a
chromatin boundary at the methylation transition. Male
autism brain
DNA samples displayed a slight increase in methylation in this transition region, suggesting a possible aberrant spreading of methylation into the MECP2 promoter in
autism males across this boundary element. In addition, autistic female brain
DNA samples showed evidence for aberrant MECP2 promoter methylation as an increase in the number of
bisulfite sequenced clones with undefined XCI status for MECP2 but not
androgen receptor (AR). To further investigate the specificity of MECP2 methylation alterations in
autism, blood
DNA samples from females and mothers of males with
autism were also examined for XCI skewing at AR, but no significant increase in XCI skewing was observed compared to controls. These results suggest that the aberrant MECP2 methylation in
autism brain
DNA samples is due to locus-specific rather than global X chromosome methylation changes.