Methylation

One other hypothesis that may account for the widespread genetic defects found in ASD patients is that there may be abnormal methylation of brain-expressed genes on the X chromosome which in turn causes abnormal expression levels of genes important during development. These alternations cause one or more genes on the single X chromosome in males to be either partially silenced or over-expressed. This similarly happens in females, but the random X-chromosome inactivation might lesson autism predisposition and prevalence in females. This proposal is consistent with the findings that males make up a significantly larger amounts of ASD cases than females.²