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Recent findings that human serum contains stably expressed microRNAs (miRNAs) have revealed a great potential of serum miRNA signature as disease fingerprints to diagnosis. Here we used genome-wide serum miRNA expression analysis to investigate the value of serum miRNAs as biomarkers for the diagnosis of Alzheimer's disease (AD). Illumina HiSeq 2000 sequencing followed by individual quantitative reverse transcriptase polymerase chain reaction (qRT-PCR) assays was used to test the difference in levels of serum miRNAs between 50 AD patients and 50 controls in the screening stages. The detected serum miRNAs then were validated by qRT-PCR in 158 patients and 155 controls. MiR-98-5p, miR-885-5p, miR-483-3p, miR-342-3p, miR-191-5p, and miR-let-7d-5p displayed significantly different expression levels in AD patients compared with controls. Among the 6 miRNAs, miR-342-3p has the best sensitivity (81.5%) and specificity (70.1%) and was correlated to Mini-Mental State Examination score. This study identified six serum miRNAs that distinguish AD patients from healthy controls with high sensitivity and specificity. Serum miRNA panel (or miR-342-3p alone) may serve as a novel, noninvasive biomarker for AD.

We conducted a replication study of the 2 genetic variants, rs11754661 and rs2073067, in MTHFD1L that have been recently reported to be associated with late-onset Alzheimer's disease (LOAD) in a genome-wide study in Caucasians. The associations were evaluated in a case-control sample comprising 1,189 Northern Han-Chinese individuals. The rs11754661 polymorphism is associated with LOAD (OR = 1.727; p = 0.016). For rs2073067, LOAD association was found only in APOEe4 carriers (OR = 0.400; p < 0.001). Haplotype analysis revealed the "AC" haplotype increased the risk of developing LOAD (OR = 1.730; p = 0.015). Our findings support a role of MTHFD1L gene in LOAD.