Cellular specificity is key to deciphering epigenetic changes underlying Alzheimer's disease.

Different cell types in the brain play distinct roles in Alzheimer's disease (AD) progression. Late onset AD (LOAD) is a complex disease, with a large genetic component, but many risk loci fall in non-coding genome regions. Epigenetics implicates the non-coding genome with control of gene expression. The epigenome is highly cell-type specific and dynamically responds to the environment. Therefore, epigenetic mechanisms are well placed to explain genetic and environmental factors that are associated with AD. However, given this cellular specificity, purified cell populations or single cells need to be profiled to avoid effect masking. Here we review the current state of cell-type specific genome-wide profiling in LOAD, covering DNA methylation (CpG, CpH, and hydroxymethylation), histone modifications, and chromatin changes. To date, these data reveal that distinct cell types contribute and react differently to AD progression through epigenetic alterations. This review addresses the current gap in prior bulk-tissue derived work by spotlighting cell-specific changes that govern the complex interplay of cells throughout disease progression and are critical in understanding and developing effective treatments for AD.

PTPN22 gene functional polymorphism (rs2476601) in older adults with frailty syndrome.

The frailty syndrome is a common clinical marker of vulnerability in older adults conducive to an overall decline in inflammatory stress responsiveness; yet little is known about the genetic risk factors for frailty in elderly. Our aim was to investigate the association between the rs2476601 polymorphism in PTPN22 gene and susceptibility to frailty in Mexican older adults. Data included 630 subjects 70 and older from The Coyoacán cohort, classified as frail, pre-frail, and non-frail following Fried's criteria. Sociodemographic and clinical characteristics were compared between groups at baseline and after a multivariate analysis. The rs2476601 polymorphism was genotyped by TaqMan genotyping assay using real-time PCR and genotype frequencies were determined for each frailty phenotype in all participants and subsets by age range. Genetic association was examined using stratified and interaction analyses adjusting for age, sex and variables selected in the multivariate analysis. Disability for day-life activities, depression and cognitive impairment were associated with the risk of pre-frailty and frailty at baseline and after adjustment. Carrying the T allele increased significantly the risk of frailty in patients 76 and older (OR 5.64, 95% CI 4.112-7.165) and decreased the risk of pre-frailty under no clinical signs of depression (OR 0.53; 95% CI 0.17-1.71). The PTPN22 polymorphism, rs2476601, could be a genetic risk factor for frailty as subject to quality of life. This is the first study analyzing such relationship in Mexican older adults. Confirming these findings requires additional association studies on wider age ranges in populations of older adults with frailty syndrome.

Analysis of the rs2476601 polymorphism of PTPN22 in Mexican mestizo patients with leprosy.

Leprosy, a human chronic granulomatous disease caused by Mycobacterium leprae (M. leprae), remains endemic in certain countries despite the use of multidrug therapy. Recently, several host genes modulating the immune responses to M. leprae infection have been suggested to influence the acquisition and clinical course of leprosy. Lymphoid protein tyrosine phosphatase, encoded by the protein tyrosine phosphatase non-receptor type 22 (PTPN22) gene, serves a negative regulatory role in T cell activation. The non-synonymous single-nucleotide polymorphism (SNP) rs2476601 (1858C>T) has been associated with autoimmune diseases. Here, the present study investigated if rs2476601 polymorphism was associated with leprosy in a Mexican mestizo population. Genotyping was performed in patients with leprosy (n=189) and control subjects (n=231) from regions with higher incidence of leprosy. Genotypic (P=0.44) and allelic frequencies (P=0.45) of the rs2476601 polymorphism were similar between patients and controls; genotypic frequencies were 91 vs. 94% for CC and 9 vs. 6% for CT, and the TT genotype was absent in both groups. Allelic frequencies were 96 vs. 97% for C, and 4 vs. 3% for T. In the same way, the genotypic (P=0.46) and allelic frequencies (P=0.47) from MB patients and controls were similar. In conclusion, there was a lack of association of the PTPN22 rs2476601 polymorphism with the development of leprosy, which suggests that this SNP was not a genetic risk factor for leprosy in the Mexican mestizo population studied.

VNTR polymorphisms of the IL-4 and IL-1RN genes and their relationship with frailty syndrome in Mexican community-dwelling elderly.

Inflammation is a key event that is closely associated with the pathophysiology of frailty. The relationship of genetic polymorphisms into inflammatory cytokines with frailty remains poorly understood. The aim of this study was to investigate the association between VNTR polymorphisms of the IL-4 and IL-1RN genes with the risk of frailty. We included a sample of 630 community-dwelling elderly aged 70 and older. Both IL-4 and IL-1RN VNTR polymorphisms were genotyped by the polymerase chain reaction (PCR) method. Mean age was 77.7 years (SD = 6.0) and 52.5 % were women. The participants classified as frail were more likely to be older, had lower MMSE score (p < 0.001), and had more disability for IADL (p < 0.001) and ADL (p < 0.001). Genotypic and allelic frequencies for the IL-4 VNTR polymorphism did not show significant differences between study groups (p > 0.05). However, we just observed a significant difference in the allelic frequencies for the A2 allele of the IL-1RN VNTR polymorphism between frail and nonfrail groups (OR 1.84, 95 % CI 1.08-3.12, p = 0.02). In addition, we analyzed the combined effect of the IL-4 and IL-1RN VNTR polymorphisms and their possible association with frailty, where the combined IL-4 (low) -IL-1Ra (high) genotype was identified as a marker of risk to frailty syndrome (OR 7.86, 95 % CI 1.83-33.69, p = 0.006). Our results suggest that both A2 allele and the combined IL-4 (low) -IL-1Ra (high) genotype might be genetic markers of susceptibility to frailty in Mexican elderly.

Lack of Association of the Polymorphisms IL-17A (-197G/A) and IL-17F (+7488A/G) with Multibacillary Leprosy in Mexican Patients.

Background. Leprosy is a chronic infectious disease caused by the intracellular acid-fast bacilli Mycobacterium leprae; it has been determined that genetic factors of the host play an important role in the disease susceptibility. Thus, in this case-control study, we evaluated the possible association between the IL-17A G-197A (rs227593) and IL-17F A7488G (His161Arg, rs763780) gene SNPs and susceptibility to leprosy disease in Mexican population. Methods. Seventy-five leprosy patients and sixty-nine control subjects were included. Both SNPs were genotyped with the polymerase chain reaction-restriction fragment length polymorphism technique. Results. We found nonsignificant differences in genotype and allele frequencies related to IL-17A G-197A (rs227593) and IL-17F A7488G (His161Arg, rs763780) gene SNPs in MB as well as subclinical forms of leprosy disease versus healthy individuals. Conclusions. Since the sample size is not large enough, it is difficult to sustain an association of susceptibility to leprosy with genotypes or allele frequencies of IL-17A G-197A (rs227593) and IL-17F A7488G (His161Arg, rs763780), suggesting that IL-17 polymorphisms have no significant role in the genetic susceptibility to development of this disease in the Mexican Mestizo population.