Under normal conditions, OPN expression is weak in the brain, while under pathological conditions including Alzheimer's disease, Parkinson's disease, TBI, stroke and hypoxia‐ischaemia brain injury, it is significantly increased in macrophages/microglia and astrocytes and exerts neuroprotective effects.26, 27, 28, 29, 30. This evidence concerns the gene SPP1 and early-onset autosomal dominant Alzheimer disease.