Previous studies using brain biopsies of patients suffering from a variety of brain tumours reported VPA concentrations, expressed as percent of plasma concentrations, ranging from 6.8 to 27.9% (0.04 to 0.20 mM) [70], which are lower than the VPA concentrations found to affect p75NTR and sortilin levels in neuronal cells. This evidence concerns the gene NGFR and brain neoplasm.