GBM cells responsive to VEGF-A signaling show a physical interaction between wild-type NRP1 and FMS-related receptor tyrosine kinase 1 (Flt-1), whereas VEGF-A-resistant GBMs show modified chondroitin-sulfated NRP-1 with no interaction with Flt-1, and eliminating the chondroitin sulfate modification in NRP-1 leads to re-sensitization to VEGF-A [97]. The gene discussed is FLT1; the disease is glioblastoma.