CDKN2A and glioblastoma: To test if the reduced survival associated with the G500 allele in the NDTMM GBM cohort was attributed to a greater loss of homozygosity or heterozygosity for p16INK4a or p14ARF, multiplex PCR was used to estimate the gene dosage of exon 1α (p16INK2A) and exon 1β (p14ARF) relative to an internal β-globin gene fragment [20].