Regarding the prevalence of asymptomatic ICAD in general population, information is still limited, in the absence of large clinical trials. ġ.2 Prognosis of asymptomatic intracranial atherosclerotic disease (ICAD) An important role in the emergence of these ethnic differences can be represented by the lifestyle: the pattern of ischemic stroke is changing in Asian patients due to the westernized lifestyle, the number of extracranial cervical disease is rising. A genome-wide linkage analysis and an exome analysis identified the strongest susceptibility gene for MMD in East Asian people: ring finger 213 (RNF213). It is also possible that misclassifying patients with adult-onset Moya-Moya disease (MMD) as having ICAD may partly explain the high prevalence of ICAD in Asians. Other studies include inherited susceptibility of intracranial vessels to atherosclerosis, acquired differences in the prevalence of risk factors, differential responses to the same risk factors, and different genetic susceptibility. The main hypotheses include: low lipid levels and high blood pressure (susceptibility to intracranial and intracerebral vascular disease) high lipids and high blood pressure (susceptibility to extracranial occlusive vascular lesions) and diabetes mellitus and metabolic syndrome (for ICAS). The reason for racial differences is still unclear. Population groups which are at high risk for ICAS include: Asians (30–50% of all new ischemic strokes), Hispanics, and population of African descent conversely, the risk is lower in Caucasians (8–10% of all new ischemic strokes). Regarding the incidence of ICAD, it varies especially by ethnicity. Intracranial arterial atherosclerotic stenosis (ICAS) represents the most advanced stage of ICAD, and thus nonstenotic ICAD is much more common than stenotic ICAD.
All major intracranial arteries are affected by atherosclerotic disease, and between 6 and 50% of all world ischemic strokes are the result of ICAD. Intracranial atherosclerosis is one of the most important causes of stroke worldwide. 1.1 The incidence of intracranial atherosclerotic disease (ICAD)