The term "hyperlipidemia" describes an extreme elevation in any of several lipid (fatty) substances in the bloodstream, as in conditions such as hypercholesterolemia and hypertriglyceridemia. Most of these disorders cause an increased risk for atherosclerosis, which is a buildup of plaque within the arterial wall that can lead to heart attacks, strokes, and gangrene. An elevated high-density (healthy) cholesterol, however, is a hyperlipidemia that protects from plaque buildup. To be called a hyperlipidemia, the value of the lipid elevation generally has to be greater than 95 percent above the average level for a person of the same age and gender in the population. Most hyperlipidemias are acquired through genes transmitted from one or both parents, although some persons may acquire a hyperlipidemia through dietary means.