Hallermann-Streiff syndrome: a rare congenital condition characterized by abnormalities of the skull and bones of the face; characteristic facial features; sparse hair; degenerative skin changes; eye abnormalities; dental defects, and proportionate short stature. Some affected people have intellectual disability. The condition has also been referred to as HSS or Hallermann Streiff Francois syndrome. The abnormal facial features can include a short, broad head (brachycephaly), a prominent forehead and/or sides of the skull (frontal bossing); a small lower jaw (micrognathia); a narrow, highly arched palate; and a thin, pinched, tapering nose (beaked nose). The genetic cause of Hallermann-Streiff syndrome is not understood and most cases occur randomly for unknown reasons (sporadically).