Main characteristics of included studies in meta-analysis.

Abbreviations: NI, no information; AD, Alzheimer's disease; SLOAD, sporadic late-onset Alzheimer's disease; SEAD, sporadic early-onset Alzheimer's disease; SAD, sporadic Alzheimer's disease; DSM, Diagnostic and Statistical Manual of Mental Disorders; * Our study; ▴Age of onset; △Included age. NINCDS-ADRDA, the National Institute of Neurological Disorders and Stoke–Alzheimer Diseases and Related Disorders Association; MMSE, mini mental state examination; ICD, International Classification of diseases; CDR, clinical dementia rating; HWE,Hardy-Weinberg equilibrium; B, balance; N, number.