Poikiloderma (a skin condition involving hypopigmentation, hyperpigmentation, spider veins and atrophy) with neutropenia (PN) is a unique clinical presentation that can be caused by mutations in the U6 snRNA biogenesis phosphodiesterase 1 gene (USB1). Curiously enough, the USB1 protein is required for U6 snRNA synthesis in yeast and zebrafish, but not humans.