The intravenous use of opioids not only increases the risk of contracting HIV and other infectious diseases but also stimulates neuroinflammation and microgliosis [292,293] and elevates levels of hyperphosphorylated tau protein, associated with leukoencephalopathy and brain atrophy, although larger-scale studies are needed to validate these findings [294,295]. The gene discussed is MAPT; the disease is Brain atrophy.