A subtype of Alzheimer's disease has been identified by neuroscientists that they say is neither well recognized nor treated appropriately. The variant, called hippocampal sparing AD, made up 11 percent of the 1,821 AD-confirmed brains examined by researchers -- suggesting this subtype is relatively widespread in the general population. It is estimated that 5.2 million Americans are living with AD. And with nearly half of hippocampal sparing AD patients being misdiagnosed, this could mean that well over 600,000 Americans make up this AD variant, researchers say.