Kato N, et al. - Researchers here examined a series of mature ovarian teratomas, complete hydatidiform moles (CHMs), struma ovarii, and extragonadal mature teratomas of females to compare their methylation profiles of imprinted genes employing a methylation-specific multiplex ligation-dependent probe amplification (MS-MLPA) method. Findings revealed differences in methylation profiles of imprinted genes between mature ovarian teratomas/struma ovarii, CHMs, and extra-ovarian teratomas. High and low methylation of maternally and paternally imprinted genes, respectively, was identified in mature ovarian teratomas, this is in concordance with their parthenogenetic origin. This pattern was recapitulated by struma ovarii, except for the adenomatous form. In CHMs, opposite overall methylation pattern was observed relative to that seen in mature ovarian teratomas, but some imprinted genes displayed aberrant methylation, indicating a relaxation of imprinting. The methylation pattern was somatic or irregular in sacrococcygeal and mediastinal mature teratomas of females. From the current concept of reprogramming in vivo, there is a likelihood that extragonadal teratomas arise from a reprogrammed somatic cell, as well as a primordial germ cells.