VDR and early-onset autosomal dominant Alzheimer disease: The older population is at an unusually high risk for vitamin D deficiency due to the decreased cutaneous synthesis, and dietary intake of vitamin D. Vitamin D receptors are widespread in brain tissue, and vitamin D's biologically active form (1,25(OH)(2)D3) has shown neuroprotective effects including the clearance of amyloid plaques, a hallmark of Alzheimer's disease [6].