Cross-cultural comparison of mild cognitive impairment between China and USA.

Individuals with mild cognitive impairment (MCI) are at increased risk for dementia of Alzheimer's type (DAT), vascular dementia (VaD), Lewy Body (LBD) and Fronto-temporal dementias (FTD). Risk factors and conversion rates of MCI to dementia have not been thoroughly investigated in developing countries. Chinese and English versions of Mini-Mental State Examination were administered serially among well-matched subjects from two clinics located in Xi'an, China and Houston, USA. Subtle cognitive impairments were weighed according to MCI criteria as defined previously. Subjects with MCI were followed for an additional 3 years after their identification. Diagnoses of VaD and DAT were made according to established criteria. During screening period, 73 American and 65 Chinese individuals were identified with MCI. After 3 years of MCI follow-up, of the 73 American MCI subjects, 35 (47.9%) developed DAT and 15 (20.5%) developed VaD. Of the 65 Chinese MCI subjects, 12 (18.5%) developed DAT and 19 (29.2%) developed VaD. According to Kaplan-Meier analysis, Chinese MCI subjects, despite their lower educational level, are 1.7 times less likely to progress to DAT and 2.3 times more likely to progress to VaD than American subjects within 3 years of MCI being identified (p<0.01). Data suggest that progression rates of MCI vary considerably among subjects from two countries. American MCI subjects are more prone to DAT, while Chinese subjects are more prone to VaD. Differences in genetic factors, cultures, educational levels, and preventive treatments of vascular risk factors are proposed as responsible for this uneven geographic distribution for different types of dementia.