PRDM9 and cancer: Of the other manually selected genes a further five exhibited a CT gene expression profile (a mixture of cancer/testis-restricted and cancer/testis/CNS-restricted); these were the meiotic recombination hotspot activator gene PRDM9, the nuclear protein in testis (NUT) gene, the testis-specific serine/threonine kinase 1 (TSSK1) gene, the synaptonemal complex component gene SYCP1 (which has previously been reported as a CT gene [18]) and the meiotic regulatory gene STRA8 (Fig. 1A).