CDKN2A and spinal meningioma: In addition, one study on sixteen patients with spinal meningiomas showed an allelic loss of the 1p chromosomal arm - involving several genes such as the ALPL (Alkaline phosphatase) gene - and a homozygous loss of 9p that results in inactivation of tumor suppressor genes such as the CDKN2A (Cyclin-dependent kinase inhibitor 2A) (19, 21).