 The role of MECP2 in disease is primarily associated with either a loss of function (under expression) of the MECP2 gene as in Rett syndrome or in a gain of function (over expression) as in MECP2 Duplication Syndrome.Many mutations have been associated with loss of expression of the MECP2 gene and have been identified in Rett syndrome patients.These mutations include changes in single DNA base pairs (SNP), insertions or deletions of DNA in the "MECP2" gene, and changes that affect how the gene information is processed into a protein (RNA splicing).