According to recent research, MCI is seen as the transitional state between cognitive changes of normal aging and Alzheimer's disease. Several studies have indicated that individuals with MCI are at an increased risk for developing AD, ranging from 1% to 25% per year; in one study 24% of MCI patients progressed to AD in 2 years and 20% more over 3 years, whereas another study indicated that the progression of MCI subjects was 55% in 4.5 years.[4][5] Some patients with MCI, however, never progress to AD.[6]