EGF and Parkinson disease: Other studies have shown that PINK1 deficiency impairs both the formation of GFAP-positive astrocytes during development and the proliferation of astrocytes upon stimulation with epidermal growth factor or fetal bovine serum (FBS).36,37 However, humans with PINK1-linked PD show elevated basal ganglia myoinositol levels by magnetic resonance spectroscopy, indicative of astrocyte proliferation within the basal ganglia.38