Credibility analysis of putative disease-causing genes using bioinformatics

Haplotype Analysis of the First A4V-SOD1 Spanish Family: Two Separate Founders or a Single Common Founder?

Despite the genetic heterogeneity reported in familial amyotrophic lateral sclerosis (ALS) (fALS), Cu/Zn superoxide-dismutase (SOD1) gene mutations are the second most common cause of the disease, accounting for around 20% of all families (ALS1) and isolated sporadic cases (sALS). At least 186 different mutations in the SOD1 gene have been reported to date. The possibility of a single founder and separate founders have been investigated for D90A (p.D91A) and A4V (p.A5V), the most common mutations worldwide. High-throughput single nucleotide polymorphism genotyping studies have suggested two founders for A4V (one for the Amerindian population and another for the European population) although the possibility that the two populations are descended from a single ancient founder cannot be ruled out. We used 15 genetic variants spanning the human chromosome 21 from the SOD1 gene to the SCAF4 gene, comparing them with the population reference panels, to demonstrate that the first A4V Spanish pedigree shared the genetic background reported in the European population.

Identification of TYW3/CRYZ and FGD4 as susceptibility genes for amyotrophic lateral sclerosis

Objective

A 2-stage genome-wide association was conducted to explore the genetic etiology of amyotrophic lateral sclerosis (ALS) in the Chinese Han population.

Methods

Totally, 700 cases and 4,027 controls were genotyped in the discovery stage using Illumina Human660W-Quad BeadChips. Top associated single nucleotide polymorphisms from the discovery stage were then genotyped in an independent cohort with 884 cases and 5,329 controls. Combined analysis was conducted by combining all samples from the 2 stages.

Results

Two novel loci, 1p31 and 12p11, showed strong associations with ALS. These novel loci explained 2.2% of overall variance in disease risk. Expression quantitative trait loci searches identified TYW/CRYZ and FGD4 as risk genes at 1p13 and 12p11, respectively.

Conclusions

This study identifies novel susceptibility genes for ALS. Identification of TYW3/CRYZ in the current study supports the notion that insulin resistance may be involved in ALS pathogenesis, whereas FGD4 suggests an association with Charcot-Marie-Tooth disease.

Burden and genotype distribution of high-risk Human Papillomavirus infection and cervical cytology abnormalities at selected obstetrics and gynecology clinics of Addis Ababa, Ethiopia

BACKGROUND

Human papillomavirus is recognized as a major cause of cervical cancer. It is estimated that annually, 7,095 women are diagnosed with cervical cancer and 4,732 die from the disease in Ethiopia. Understanding that the screening practice is very poor and the coverage is very limited, this disease burden is one of the major public health agendas in Ethiopia. This study aimed to assess the burden and genotype distribution of high-risk human papillomavirus (HR HPV) infection and cervical cytology abnormalities at selected obstetrics and gynecology clinics of Addis Ababa, Ethiopia.

METHODS

An institutional-based cross-sectional study design was employed from June to October 2015. Cervical samples were collected from 366 participants based on inclusion criteria. HR HPV DNA was analyzed using an Abbott Real-Time PCR system, and cervical cytology screening was performed using the conventional Pap-smear technique. Data were entered in to Epi-data version 13 and analyzed using STATA version 11.

RESULTS

The overall HR HPV burden and abnormal cytology were 13.7 and 13.1%, respectively. The majority of HR HPV types were other than types 16 and 18. Of the total abnormal cytology results, 81.3% were low-grade squamous intraepithelial lesions (LSILs), and 12.5 and 6.3% were atypical squamous cells of undetermined significance (ASCUS) and high-grade squamous intraepithelial lesions (HSILs), respectively. Residence, occupation, and HIV serostatus were significantly associated with HR HPV infection. Among the variables, age, age at first marriage, and education were the only ones associated with cervical cytology abnormalities. The overall agreement between the real-time PCR and Pap cytology screening methods was 78.96% (Kappa value of 0.12, 95% CI (0.00-0.243), P = 0.01).

CONCLUSIONS

Non-16/18 HR HPV genotypes represented the largest proportion of HR HPV infections in this study. Women without cervical cytology abnormalities had the highest frequency of HR HPV infection. A large-scale community-based cohort study shall be designed and implemented to further identifying the persistent genotype and assessing the changes in cervical epithelial cell lines.

Whole exome sequencing and DNA methylation analysis in a clinical amyotrophic lateral sclerosis cohort

Background

Gene discovery has provided remarkable biological insights into amyotrophic lateral sclerosis (ALS). One challenge for clinical application of genetic testing is critical evaluation of the significance of reported variants.

Methods

We use whole exome sequencing (WES) to develop a clinically relevant approach to identify a subset of ALS patients harboring likely pathogenic mutations. In parallel, we assess if DNA methylation can be used to screen for pathogenicity of novel variants since a methylation signature has been shown to associate with the pathogenic C9orf72 expansion, but has not been explored for other ALS mutations. Australian patients identified with ALS‐relevant variants were cross‐checked with population databases and case reports to critically assess whether they were “likely causal,” “uncertain significance,” or “unlikely causal.”

Results

Published ALS variants were identified in >10% of patients; however, in only 3% of patients (4/120) could these be confidently considered pathogenic (in SOD1 and TARDBP). We found no evidence for a differential DNA methylation signature in these mutation carriers.

Conclusions

The use of WES in a typical ALS clinic demonstrates a critical approach to variant assessment with the capability to combine cohorts to enhance the largely unknown genetic basis of ALS.

RNAseq Analyses Identify Tumor Necrosis Factor-Mediated Inflammation as a Major Abnormality in ALS Spinal Cord

ALS is a rapidly progressive, devastating neurodegenerative illness of adults that produces disabling weakness and spasticity arising from death of lower and upper motor neurons. No meaningful therapies exist to slow ALS progression, and molecular insights into pathogenesis and progression are sorely needed. In that context, we used high-depth, next generation RNA sequencing (RNAseq, Illumina) to define gene network abnormalities in RNA samples depleted of rRNA and isolated from cervical spinal cord sections of 7 ALS and 8 CTL samples. We aligned >50 million 2X150 bp paired-end sequences/sample to the hg19 human genome and applied three different algorithms (Cuffdiff2, DEseq2, EdgeR) for identification of differentially expressed genes (DEG's). Ingenuity Pathways Analysis (IPA) and Weighted Gene Co-expression Network Analysis (WGCNA) identified inflammatory processes as significantly elevated in our ALS samples, with tumor necrosis factor (TNF) found to be a major pathway regulator (IPA) and TNFα-induced protein 2 (TNFAIP2) as a major network "hub" gene (WGCNA). Using the oPOSSUM algorithm, we analyzed transcription factors (TF) controlling expression of the nine DEG/hub genes in the ALS samples and identified TF's involved in inflammation (NFkB, REL, NFkB1) and macrophage function (NR1H2::RXRA heterodimer). Transient expression in human iPSC-derived motor neurons of TNFAIP2 (also a DEG identified by all three algorithms) reduced cell viability and induced caspase 3/7 activation. Using high-density RNAseq, multiple algorithms for DEG identification, and an unsupervised gene co-expression network approach, we identified significant elevation of inflammatory processes in ALS spinal cord with TNF as a major regulatory molecule. Overexpression of the DEG TNFAIP2 in human motor neurons, the population most vulnerable to die in ALS, increased cell death and caspase 3/7 activation. We propose that therapies targeted to reduce inflammatory TNFα signaling may be helpful in ALS patients.

Large-scale screening in sporadic amyotrophic lateral sclerosis identifies genetic modifiers in C9orf72 repeat carriers

Sporadic amyotrophic lateral sclerosis (ALS) is considered to be a complex disease with multiple genetic risk factors contributing to the pathogenesis. Identification of genetic risk factors that co-occur frequently could provide relevant insight into underlying mechanisms of motor neuron degeneration. To dissect the genetic architecture of sporadic ALS, we undertook a large sequencing study in 755 apparently sporadic ALS cases and 959 controls, analyzing 10 ALS genes: SOD1, C9orf72, TARDBP, FUS, ANG, CHMP2B, ATXN2, NIPA1, SMN1, and UNC13A. We observed sporadic cases with multiple genetic risk variants in 4.1% compared with 1.3% in controls. The overall difference was not in excess of what is to be expected by chance (binomial test, p = 0.59). We did, however, observe a higher frequency than expected of C9orf72 repeat carriers with co-occurring susceptibility variants (ATXN2, NIPA1, and SMN1; p = 0.001), which is mainly because of the co-occurrence of NIPA1 repeats in 15% of C9orf72 repeat carriers (p = 0.006).