Among these are, for instance, males with Klinefelter syndrome (i.e., they have one Y chromosome and two X chromosomes), who have one X chromosome with a mutated MECP2 gene, as well as males, who have mosaic MECP2 mutations (i.e., cells containing the MECP2 mutation exist alongside a normal cell line). The gene discussed is MECP2; the disease is Klinefelter syndrome.