Atherosclerosis is a pattern of the disease arteriosclerosis, characterized by development of abnormalities called lesions in walls of arteries. These lesions may lead to narrowing of the arterial walls due to buildup of atheromatous plaques. At onset there are usually no symptoms, but if they develop, symptoms generally begin around middle age. In severe cases, it can result in coronary artery disease, stroke, peripheral artery disease, or kidney disorders, depending on which body part(s) the affected arteries are located in the body. The exact cause of atherosclerosis is unknown and is proposed to be multifactorial. Risk factors include abnormal cholesterol levels, elevated levels of inflammatory biomarkers, high blood pressure, diabetes, smoking (both active and passive smoking), obesity, genetic factors, family history, lifestyle habits, and an unhealthy diet. Plaque is made up of fat, cholesterol, calcium, and other substances found in the blood. The narrowing of arteries limits the flow of oxygen-rich blood to parts of the body. Diagnosis is based upon a physical exam, electrocardiogram, and exercise stress test, among others. Prevention guidelines include, eating a healthy diet, exercising, not smoking, and maintaining normal body weight. Treatment of established disease may include medications to lower cholesterol such as statins, blood pressure medication, and anticoagulant therapies to reduce the risk of blood clot formation. As the disease state progresses more invasive strategies are applied such as percutaneous coronary intervention, coronary artery bypass graft, or carotid endarterectomy. Genetic factors are also strongly implicated in the disease process; it is not entirely based on lifestyle choices. Atherosclerosis generally starts when a person is young and worsens with age. Almost all people are affected to some degree by the age of 65. It is the number one cause of death and disability in developed countries. Though it was first described in 1575, there is evidence suggesting that this disease state is genetically inherent in the broader human population, with its origins tracing back to genetic mutations that may have occurred more than two million years ago during the evolution of hominin ancestors of modern human beings.

Reference
Wiki: Atherosclerosis