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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.

Genetic factors play an important role in the Alzheimer's disease (AD) development and memory impairment is a cardinal clinical feature of AD. Kidney and brain expressed protein (KIBRA), owing to its connection with human episodic memory, became an interesting candidate gene for AD. Recently, KIBRA (rs17070145) was reported to be associated with AD in the genetic and functional levels in Caucasian and African-American, and the association might be different across age groups. To investigate the possibility of age-dependent association of KIBRA with AD in Asian, we conducted an independent replication study in a cohort of 1,586 subjects from Han Chinese (including 790 LOAD patients and 796 healthy controls). The results revealed no significant differences in the distributions of genotype or allele between LOAD and control groups in the total sample. However, when these data were stratified by their age, we observed a significant difference in the genotypes and alleles frequencies (genotype: p = 0.004, allele: p = 0.035) in the young subgroup. Moreover, the association was further demonstrated in logistic regression analysis (rs17070145: p = 0.045, OR = 0.428). Our data suggested that KIBRA might associate with younger AD patients (≤74 years) in a Northern Han Chinese population.

Mitochondrial dysfunction is an early defect in the pathogenesis of late-onset Alzheimer's disease (LOAD). One interesting candidate gene for mitochondrial dysfunction in LOAD is the translocase of outer mitochondrial membrane 40 homolog (TOMM40) gene. Several single nucleotide polymorphisms (SNPs) within TOMM40 have been shown to affect susceptibility to LOAD in Caucasians, while there are no studies on the association of the polymorphisms with LOAD risk in Han Chinese. Here, the association of TOMM40 polymorphisms in LOAD was investigated in a large Northern Han Chinese cohort consisting of 1,578 individuals. Both allelic and genotypic associations of three SNPs (rs157580, rs2075650, and rs11556505) with LOAD risk were observed in the total sample as well as in the non- APOE ε4 carriers. For rs1160985, the allele and genotype frequencies differed significantly only in APOE ε4 carriers. After adjustment for age, gender, and APOE ε4 status, the association remained statistically significant only for the rs157580 but not for rs2075650 and rs11556505. In contrast, the rs1160985 exhibited significant risk effect after adjustment. In addition, haplotype analysis confirmed that the haplotypes derived from SNPs in rs2075650, rs11556505, and rs1160985 were associated with either risk or protective effects. In summary, our findings suggest that the TOMM40 polymorphisms may play a role in the pathogenesis of LOAD in Han Chinese.

Sortilin-related VPS domain containing receptor 1 (SORCS1), is located on chromosome 10q23.3, a chromosomal region of interest in Alzheimer's disease (AD) defined by many genome-wide and chromosome10-specific studies. Recently, three intronic variants (rs12571141, rs17277986 and rs6584777) within SORCS1 were reported to be associated with AD in Caucasian. In order to assess the involvement of the SORCS1 polymorphisms in the progression of late-onset AD (LOAD), we conducted an independent replication study in 1198 unrelated Northern Han Chinese subjects comprising 598 LOAD patients and 600 healthy controls matched for gender and age. The results revealed no significant differences in the distributions of genotype or allele between LOAD and control groups in the total sample. However, when these data were stratified by the Apolipoprotein E (APOE) e4 status, we observed significant differences in the genotypes and allele frequencies (rs12571141: P = 0.001, rs17277986: P = 0.005, rs6584777: P = 0.023) in APOE e4 allele carriers. Moreover, the association was further demonstrated in logistic regression analysis (rs12571141: P = 0.002, OR = 0.424; rs17277986: P = 0.004, OR = 0.447; rs6584777: P = 0.019, OR = 0.523) and haplotype analysis (GCC: P = 0.002, ATT: P = 0.002, ACC: P = 0.025) in this subset. Our data suggested that SORCS1 was in interaction with APOE in the development of LOAD in a Northern Han Chinese population.

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.

Background MicroRNAs (miRNAs) are endogenous small RNAs of 21–25 nucleotides that post-transcriptionally regulate gene expressions. Recently, circulating miRNAs have been reported as promising biomarkers for neurodegenerative disorders and processes affecting the central nervous system. This study was conducted to investigate the potential role of serum miRNAs as diagnostic biomarkers for Alzheimer's disease (AD). Methods Serum samples were obtained from 105 probable AD patients and 150 age- and gender-matched normal controls. The serum concentrations of miRNAs miR-9, miR-29a, miR-29b, miR-101, miR-125b, and miR-181c were measured with a real-time quantitative reverse transcriptase PCR (qRT-PCR) method. Results We found both miR-125b and miR-181c were down-regulated while miR-9 was up-regulated in serum of AD patients compared with that of normal controls. Among the receiver operating characteristic (ROC) results, miR-125b alone showed its priority with a specificity up to 68.3% and a sensitivity of 80.8%. Importantly, miR-125b was correlated with the Mini Mental State Examination (MMSE) in AD patients. Conclusions Our results indicate that serum miR-125b may serve as a useful noninvasive biomarker for AD.

Both Alzheimer's disease (AD) and progressive supranuclear palsy (PSP) are a class of neurodegenerative diseases associated with the pathologic aggregation of tau protein in the human brain. They share some clinical and pathologic characteristics. A recent genome-wide association study reported several single-nucleotide polymorphisms at the STX6, MOBP, MAPT, and EIF2AK3 in association with PSP. To explore whether these single-nucleotide polymorphisms are associated with AD risk, we conducted a case-control study to investigate the PSP-associated loci in 1592 Han Chinese subjects. Rs242557 at the MAPT locus was associated with late-onset AD (LOAD) (odds ratio [OR], 1.175; p = 0.026), which appeared to be stronger for LOAD patients with apolipoprotein E (APOE) e4 allele (OR, 1.510), and this positive association was not changed after adjusting for age, sex, and the APOE e4-carrier status (additive model: OR, 1.163; p = 0.036; dominant model: OR, 1.315; p = 0.010). Rs1768208 in MOBP and rs7571971 in EIF2AK3 showed association only in the APOE e4 positive subjects, and these did not appear to be independent of APOE. As for rs1411478 in STX6, we did not explore any association with LOAD. Our exploratory analysis mainly suggests an association of MAPT with LOAD, especially in APOE e4 carriers. Genotypes at MOBP and EIF2AK3 confer risk predominantly in APOE e4-positive subjects, with indications of an interaction between APOE and MOBP or EIF2AK3 on AD risk.

Objective Five genomewide association studies (GWAS) in white populations have recently identified and confirmed 9 novel Alzheimer's disease (AD) susceptibility loci ( CLU , CR1 , PICALM, BIN1 , ABCA7 , MS4A gene cluster, CD2AP , CD33, and EPHA1 ). These studies have been conducted almost exclusively in white populations and it is unclear whether these observations generalize to populations with different ethnicities. Methods We recruited 1224 unrelated northern Han Chinese subjects comprising 612 patients with a clinical diagnosis of late-onset AD (LOAD) according to the criteria of the National Institute of Neurological and Communicative Diseases and Stroke/Alzheimer's Disease and Related Disorders Association and 612 healthy age- and sex-matched control subjects. Because of our previous study investigating CLU, CR1, and PICALM in the Han population, we limited the current analysis to BIN1 , ABCA7 , MS4A gene cluster, CD2AP , CD33 , and EPHA1 . Results In a multivariate analysis, associations of MS4A6A (rs610932; odds ratio=0.632, Bonferroni corrected P = .019) and CD33 (rs3865444; odds ratio=1.492, Bonferroni corrected P = .017) with LOAD were replicated successfully. When these data were stratified by apolipoprotein E ( APOE ) e4 status, both rs610932 and rs610932 were evident only among subjects without the APOE e4 allele. For BIN1 , assuming a dominant model of inheritance, a positive association for rs7561528 in APOE e4 carriers was observed. This association, however, did not remain significant after Bonferroni correction. As for ABCA7 , CD2AP, and EPHA1 single nucleotide polymorphisms from recent GWAS, despite the similar directional effects, no significant differences in genotype and estimated allele frequency distribution between patients and control subjects were observed. Conclusions This study provides the first independent evidence that MS4A and CD33 loci are associated with the risk of LOAD in northern Han Chinese population. Genotypes at the two loci confer risk predominantly in APOE e4-negative subjects.