NF2 and meningioma: Genetic alterations of the Nf2 gene are present in 60% of sporadic meningiomas regardless of grade, suggesting their initiating role in meningeal tumorigenesis; meanwhile, CDKN2A (p16INK4a), p14ARF, and CDKN2B (p15INK4b) are thought to be responsible for progression to higher grades of meningioma.