PLOD1 and Alzheimer disease: Peripheral LH levels correlate with AD progression, Aβ load, and cognitive decline in humans (106, 107), but it is unclear if this effect is through a direct action of LH on neurons after crossing the BBB, an indirect action by which high peripheral concentrations of LH suppress brain synthesis of LH, or an entrance of peripheral LH to the brain only after damage to the BBB.