Fetiform teratoma was a parthenogenetic tumor arising from a mature ovum

The aim of this study was to investigate the parthenogenetic origin of fetiform teratoma by using molecular genetic studies and methylation status analyses. A fetiform teratoma was removed from a 35-year-old nulligravida woman. Genotyping of microsatellite marker loci, microarray analysis of single-nucleotide polymorphism (SNP) loci and methylation status analysis of the differentially methylated region (DMR) within the human IGF2-H19 locus were performed. Karyotypes of the host and the fetiform teratoma were 46, XX. The fetiform teratoma was homozygous at all loci and meiotic recombinations in the tumor were confirmed by SNP microarray analysis. Methylation analysis indicated that the host had both methylated and unmethylated IGF2-H19 DMR alleles, while the fetiform teratoma had unmethylated alleles only. Genetically, the fetiform teratoma had homozygous genotypes with meiotic recombination and a duplicated unmethylated host allele, indicating that it was a parthenogenetic tumor arising from a mature ovum after meiosis II. This is the first demonstration of a fetiform teratoma originating from a mature haploid ovum.