Interestingly, at ages of 15–30 weeks, an estimated 10% of the animals in the GFAP-Cre; PdgfrαK/+; INK4A/Arf−/− cohort displayed an enlarged skull and apparent neurological symptoms (Fig. S3c), indicative of advanced primary brain tumors (see below). This evidence concerns the gene CDKN2A and brain neoplasm.