The large numbers and nuclear morphology of the cells staining with DUX4 in the seminiferous tubules, together with expression of DUX4 in the human germ-cell cell tumor lines SuSa and 833K [14] (data not shown), leads us to conclude that DUX4 is expressed in the germ-line lineage. The gene discussed is DUX4; the disease is germ cell tumor.