The Polycomb group of (Pc-G) genes and trithorax group of genes are known to play a crucial role in the maintenance of the transcriptional repression state of Hox genes, probably through modification of the chromatin configuration. The rae28/mph1 gene is a mammalian homologue of the Drosophila polyhomeotic gene, which belongs to the Pc-G genes. As reported previously, we established mice deficient in the rae28/mph1 gene and showed that these homozygous animals displayed the developmental defects compatible with a human congenital disorder, CATCH22 syndrome. In this study we analyzed the structural organization of the human counterpart of the rae28/mph1 gene (RAE28/HPH1) and its processed pseudogene (psiPH), which are located on, respectively, human chromosome 12p13 and 12q13. The HPH1 gene consists of 15 exons spanning approximately 26 kb and its structural organization is well conserved between mouse and human. These genetic information of the RAE28/HPH1 gene may provide an important clue for further examination of its involvement in human congenital disorders related to CATCH22 syndrome.