Cascade of interactions between candidate genes reveals convergent mechanisms in keratoconus disease pathogenesis

Keratoconus is a progressive thinning, steepening and distortion of the cornea which can lead to loss of vision if left untreated. Keratoconus has a complex multifactorial etiology, with genetic and environmental components contributing to the disease pathophysiology. Studies have observed high concordance between monozygotic twins, discordance between dizygotic twins, and high familial segregation indicating the presence of a very strong genetic component in the pathogenesis of keratoconus. The use of genome-wide linkage studies on families and twins, genome-wide association studies (GWAS) on case-controls, next-generation sequencing (NGS)-based genomic screens on both familial and non-familial cohorts have led to the identification of keratoconus candidate genes with much greater success and increased resproducibility of genetic findings. This review focuses on candidate genes identified till date and attempts to understand their role in biological processes underlying keratoconus pathogenesis. In addition, using these genes I propose molecular pathways that could contribute to keratoconus pathogenesis. The pathways identified the presence of direct cross-talk between known candidate genes of keratoconus and remarkably, 28 known candidate genes have a direct relationship among themselves that involves direct protein-protein binding, regulatory activities such as activation and inhibition, chaperone, transcriptional activation/co-activation, and enzyme catalysis. This review attempts to describe these relationships and cross-talks in the context of keratoconus pathogenesis.

Identification of primary copy number variations reveal enrichment of Calcium, and MAPK pathways sensitizing secondary sites for autism

Background

Autism is a neurodevelopmental condition with genetic heterogeneity. It is characterized by difficulties in reciprocal social interactions with strong repetitive behaviors and stereotyped interests. Copy number variations (CNVs) are genomic structural variations altering the genomic structure either by duplication or deletion. De novo or inherited CNVs are found in 5–10% of autistic subjects with a size range of few kilobases to several megabases. CNVs predispose humans to various diseases by altering gene regulation, generation of chimeric genes, and disruption of the coding region or through position effect. Although, CNVs are not the initiating event in pathogenesis; additional preceding mutations might be essential for disease manifestation. The present study is aimed to identify the primary CNVs responsible for autism susceptibility in healthy cohorts to sensitize secondary-hits. In the current investigation, primary-hit autism gene CNVs are characterized in 1715 healthy cohorts of varying ethnicities across 12 populations using Affymetrix high-resolution array study. Thirty-eight individuals from twelve families residing in Karnataka, India, with the age group of 13–73 years are included for the comparative CNV analysis. The findings are validated against global 179 autism whole-exome sequence datasets derived from Simons Simplex Collection. These datasets are deposited at the Simons Foundation Autism Research Initiative (SFARI) database.

Results

The study revealed that 34.8% of the subjects carried 2% primary-hit CNV burden with 73 singleton-autism genes in different clusters. Of these, three conserved CNV breakpoints were identified with ARHGAP11B, DUSP22, and CHRNA7 as the target genes across 12 populations. Enrichment analysis of the population-specific autism genes revealed two signaling pathways—calcium and mitogen-activated protein kinases (MAPK) in the CNV identified regions. These impaired pathways affected the downstream cascades of neuronal function and physiology, leading to autism behavior. The pathway analysis of enriched genes unravelled complex protein interaction networks, which sensitized secondary sites for autism. Further, the identification of miRNA targets associated with autism gene CNVs added severity to the condition.

Conclusion

These findings contribute to an atlas of primary-hit genes to detect autism susceptibility in healthy cohorts, indicating their impact on secondary sites for manifestation.

Placental epigenetics for evaluation of fetal congenital heart defects: Ventricular Septal Defect (VSD)

Ventricular Septal Defect (VSD), the most common congenital heart defect, is characterized by a hole in the septum between the right and left ventricles. The pathogenesis of VSD is unknown in most clinical cases. There is a paucity of data relevant to epigenetic changes in VSD. The placenta is a fetal tissue crucial in cardiac development and a potentially useful surrogate for evaluating the development of heart tissue. To understand epigenetic mechanisms that may play a role in the development of VSD, genome-wide DNA methylation assay on placentas of 8 term subjects with isolated VSD and no known or suspected genetic syndromes and 10 unaffected controls was performed using the Illumina HumanMethylation450 BeadChip assay. We identified a total of 80 highly accurate potential CpGs in 80 genes for detection of VSD; area under the receiver operating characteristic curve (AUC ROC) 1.0 with significant 95% CI (FDR) p-values < 0.05 for each individual locus. The biological processes and functions for many of these differentially methylated genes are previously known to be associated with heart development or disease, including cardiac ventricle development (HEY2, ISL1), heart looping (SRF), cardiac muscle cell differentiation (ACTC1, HEY2), cardiac septum development (ISL1), heart morphogenesis (SRF, HEY2, ISL1, HEYL), Notch signaling pathway (HEY2, HEYL), cardiac chamber development (ISL1), and cardiac muscle tissue development (ACTC1, ISL1). In addition, we identified 8 microRNAs that have the potential to be biomarkers for the detection of VSD including: miR-191, miR-548F1, miR-148A, miR-423, miR-92B, miR-611, miR-2110, and miR-548H4. To our knowledge this is the first report in which placental analysis has been used for determining the pathogenesis of and predicting VSD.

Newborn blood DNA epigenetic variations and signaling pathway genes associated with Tetralogy of Fallot (TOF)

Tetralogy of Fallot (TOF) is the most common Critical Congenital Heart Defect (CCHD). The etiology of TOF is unknown in most cases. Preliminary data from our group and others suggest that epigenetic changes may play an important role in CHD. Epidemiologically, a significant percentage of CHD including TOF fail to be diagnosed in the prenatal and early newborn period which can negatively affect health outcomes. We performed genome-wide methylation assay in newborn blood in 24 non-syndromic TOF cases and 24 unaffected matched controls using Illumina Infinium HumanMethylation450 BeadChips. We identified 64 significantly differentially methylated CpG sites in TOF cases, of which 25 CpG sites had high predictive accuracy for TOF, based on the area under the receiver operating characteristics curve (AUC ROC) ≥ 0.90). The CpG methylation difference between TOF and controls was ≥10% in 51 CpG targets suggesting biological significance. Gene ontology analysis identified significant biological processes and functions related to these differentially methylated genes, including: CHD development, cardiomyopathy, diabetes, immunological, inflammation and other plausible pathways in CHD development. Multiple genes known or plausibly linked to heart development and post-natal heart disease were found to be differentially methylated in the blood DNA of newborns with TOF including: ABCB1, PPP2R5C, TLR1, SELL, SCN3A, CREM, RUNX and LHX9. We generated novel and highly accurate putative molecular markers for TOF detection using leucocyte DNA and thus provided information on pathogenesis of TOF.

Complex interaction between mutant HNRNPA1 and gE of varicella zoster virus in pathogenesis of multiple sclerosis

Multiple sclerosis (MS) is a demyelinating disease of the central nervous system causing axonal injury, neuronal loss, and atrophy of the central nervous system leading to permanent neurological and clinical disability. Presence of mutations in M9 domain of HNRNPA1 and detection of autoantibodies against this domain in HNRNPA1 qualifies it as a strong candidate for causing MS. These two aspects indicate the presence of a facilitator in associating them. Varicella zoster virus (VZV), known to cause chicken pox infection in humans, is a significant contender in sensitizing the infected people towards MS. Reactivation of latent herpes viruses by other infectious agents and cross-recognition of common viral antigens with antigens found in the myelin sheath induces molecular mimicry or superantigens. Mutations in HNRNPA1 cause mislocalization to the cytoplasm, and co-localize with stress granules (SG) causing cellular apoptosis, this creates the first step toward MS pathogenesis. Mutant HNRNPA1 accumulates in SG allowing the cells to display peptides of HNRNPA1 on surfaces of major histocompatibility complex (MHC) I triggering a cascade of immune reactions. Since glycoprotein E (gE) of VZV shares >62% amino acids sequence similarity with Prion-like domain (PrLD) of HNRNPA1, signifying the reason behind autoantibodies against M9 and PrLD of HNRNPA1. This review attempts to delineate the interactions of VZV, gE of VZV, with M9 domain and PrLD of HNRNPA1 in a step-by-step process. This supports the tripartite model that an environmental trigger in genetically susceptible individuals causes an autoimmune response to self-CNS antigens that result in the pathology observed in the brain and spinal cord of MS patients.

Dysregulation of NRXN1 by mutant MIR8485 leads to calcium overload in pre-synapses inducing neurodegeneration in Multiple sclerosis

OBJECTIVES

To identify Damaging mutations in microRNAs (miRNAs) and 3' untranslated regions (UTRs) of target genes to establish Multiple sclerosis (MS) disease pathway.

METHODS

Female aged 16, with Relapsing Remitting Multiple sclerosis (RRMS) was reported with initial symptoms of blurred vision, severe immobility, upper and lower limb numbness and backache. Whole Exome Sequencing (WES) and disease pathway analysis was performed to identify mutations in miRNAs and UTRs.

RESULTS

We identified Deleterious/Damaging multibase mutations in MIR8485 and NRXN1. miR-8485 was found carrying frameshift homozygous deletion of bases CA, while NRXN1 was found carrying nonframeshift homozygous substitution of bases CT to TC in exon 8 replacing Serine with Leucine.

CONCLUSIONS

Mutations in miR-8485 and NRXN1 was found to alter calcium homeostasis and NRXN1/NLGN1 cell adhesion molecule binding affinities. The miR-8485 mutation leads to overexpression of NRXN1 altering pre-synaptic Ca²⁺ homeostasis, inducing neurodegeneration.

Identifying the risk of producing aneuploids using meiotic recombination genes as biomarkers: A copy number variation approach

Background & objectives:

Aneuploids are the most common chromosomal abnormality in liveborns and are usually the result of non-disjunction (NDJ) in meiosis. Copy number variations (CNVs) are large structural variations affecting the human genome. CNVs influence critical genes involved in causing NDJ by altering their copy number which affects the clinical outcome. In this study influence of CNVs on critical meiotic recombination was examined using new computational technologies to assess their role in causing aneuploidy.

Methods:

This investigation was based on the analysis of 12 random normal populations consisting of 1714 individuals for aneuploid causing genes under CNV effect. To examine the effect of CNVs on genes causing aneuploidy, meiotic recombination genes were analyzed using EnrichR, WebGestalt and Ingenuity Pathway Analysis (IPA).

Results:

Forty three NDJ genes were found under CNV burden; IPA (Ingenuity Pathway Analysis) and KEGG (Kyoto Encyclopedia of Genes and Genomes) pathway analysis of CNV in meiotic recombination genes revealed a significant role of breast cancer gene 1, amyloid protein precursor, mitogen-activated protein kinase and nerve growth factor as key molecular players involved in causing aneuploidy. Interaction between these genes with other CNV-overlapping genes involved in cell cycle, recombination and meiosis might lead to increased incidences of aneuploidy.

Interpretation & conclusions:

The findings of this study implied that the effect of CNVs on normal genome contributed in amplifying the occurrences of chromosomal aneuploidies. The normal individuals consisting of variations in the susceptible genes causing aneuploids in the population remain undetected until the disorder genes express in the succeeding generations.

High-resolution arrays reveal burden of copy number variations on Parkinson disease genes associated with increased disease risk in random cohorts

BACKGROUND

Parkinson disease (PD) is a neurological disease responsible for a considerable rate of mortality and morbidity in the society. Since the symptoms of the disease appear much later than the actual onset of neuron degeneration, a majority of cases remain undiagnosed until the manifestation of the symptoms.

OBJECTIVES

In order to investigate the existence of such susceptibility in the population, we analyzed Copy Number Variation (CNV) influences on PD genes in 1715 individuals from 12 different populations.

RESULTS

Overall, 16 CNV-PD genes, 3 known to be causal and 13 associated, were found to be significantly enriched. PARK2, was under heavy burden with ~1% of the population containing CNV in the exonic region. The impact of these genes on the genome and disease pathway was analyzed using several genome analysis tools. Protein interaction network of CNV-PD genes revealed a complex interaction of molecules forming a major hub by the α-Synuclein, whose direct interactors, LRRK2, PARK2 and ATP13A2 are under CNV influence.

CONCLUSIONS

We hypothesize that CNVs may not be the initiating event in the pathogenesis of PD and remain latent until additional secondary hits are acquired and also propose novel genes that may fall under the PD pathway which contribute in pathogenesis.

Global spectrum of copy number variations reveals genome organizational plasticity and proposes new migration routes

Global spectrum of CNVs is required to catalog variations to provide a high-resolution on the dynamics of genome-organization and human migration. In this study, we performed genome-wide genotyping using high-resolution arrays and identified 44,109 CNVs from 1,715 genomes across 12 populations. The study unraveled the force of independent evolutionary dynamics on genome-organizational plasticity across populations. We demonstrated the use of CNV tool to study human migration and identified a second major settlement establishing new migration routes in addition to existing ones.

Genetic Epidemiology Studies on Unusual Genetic Morphophenotypes in a Settled Community from South India

Genetic disorders in a population can be caused in many ways and these genetic disorders are heritable, and are passed down the generations. These disorders are complex, multifactorial, or polygenic, and are associated with the effects of multiple genes in combination with lifestyles and environmental factors. Familial aggregation approach and segregation approach was used in this study to identify the prevalent genetic conditions and their inheritance patterns. Here, we report a population which had a very high number of unusual genetic morphophenotypes. We observed that these unusual morphophenotypes in this population are a result of an interaction between “inbreeding, consanguinity and accumulating mutations”. Statistical analysis revealed that individuals in this population carry more than 20 deleterious recessive genes based on Slatis method of calculating abnormal autosomal recessive genes in individuals.

Copy number variation burden on asthma subgenome in normal cohorts identifies susceptibility markers

PURPOSE

Asthma is a complex disease caused by interplay of genes and environment on the genome of an individual. Copy number variations (CNVs) are more common compared to the other variations that disrupt genome organization. The effect of CNVs on asthma subgenome has been less studied compared to studies on the other variations. We report the assessments of CNV burden in asthma genes of normal cohorts carried out in different geographical areas of the world and discuss the relevance of the observation with respect to asthma pathogenesis.

METHODS

CNV analysis was performed using Affymerix high-resolution arrays, and various bioinformatics tools were used to understand the influence of genes on asthma pathogenesis.

RESULTS

This study identified 61 genes associated with asthma and provided various mechanisms and pathways underlying asthma pathogenesis. CCL3L1, ADAM8, and MUC5B were the most prevalent asthma genes. Among them, CCL3L1 was found across all 12 populations in varying copy number states. This study also identified the inheritance of asthma-CNVs from parents to offspring creating the latent period for manifestation of asthma.

CONCLUSIONS

This study revealed CNV burden with varying copy number states and identified susceptibility towards the disease manifestation. It can be hypothesized that primary CNVs may not be the initiating event in the pathogenesis of asthma and additional preceding mutations or CNVs may be required. The initiator or primary CNVs sensitize normal cohorts leading to an increased probability of accumulating mutations or exposure to allergic stimulating agents that can augment the development of asthma.

Insertion-deletions burden in copy number polymorphisms of the Tibetan population

BACKGROUND:

Many studies have been conducted to identify either insertions-deletions (inDels) or copy number variations (CNVs) in humans, but few studies have been conducted to identify both of these forms coexisting in the same region.

AIMS AND OBJECTIVES:

To map the functionally significant sites within human genes that are likely to influence human traits and diseases.

MATERIALS AND METHODS:

In this report, we describe an inDel map in the 1051 Tibetan CNV regions obtained through CNV genotyping using Affymetrix Genome-wide single nucleotide polymorphism 6.0 chip. InDel polymorphisms in these copy number polymorphism regions were identified with a computational approach using the 2500 deoxyribonucleic acid sequences obtained from the 1000 Genome Project.

RESULTS:

The study identified a total of 95935 inDels that range from 1 bp to several bps in length which were found scattered across regulatory regions, exons and in introns of genes underlying the CNVs. A study on the distribution of inDels revealed that the majority of inDels were found in coding regions of the genome than the noncoding, while within the genes, inDels in intron regions were more followed by exonic regions and finally the regulatory regions.

CONCLUSION:

Study of inDels in CNV regions contribute to the enhanced understanding of the role played by the two variations and their collective influence on the genome. Further, a collection of these inDel genetic markers will aid in genetic mapping, further understanding of the phenotypic variability, identification of disease genes and in detecting novel CNVs.

Family based genome-wide copy number scan identifies complex rearrangements at 17q21.31 in dyslexics

Developmental dyslexia (DD) is a complex heritable disorder with unexpected difficulty in learning to read and spell despite adequate intelligence, education, environment, and normal senses. We performed genome-wide screening for copy number variations (CNVs) in 10 large Indian dyslexic families using Affymetrix Genome-Wide Human SNP Array 6.0. Results revealed the complex genomic rearrangements due to one non-contiguous deletion and five contiguous micro duplications and micro deletions at 17q21.31 region in three dyslexic families. CNVs in this region harbor the genes KIAA1267, LRRC37A, ARL17A/B, NSFP1, and NSF. The CNVs in case 1 and case 2 at this locus were found to be in homozygous state and case 3 was a de novo CNV. These CNVs were found with at least one CNV having a common break and end points in the parents. This cluster of genes containing NSF is implicated in learning, cognition, and memory, though not formally associated with dyslexia. Molecular network analysis of these and other dyslexia related module genes suggests NSF and other genes to be associated with cellular/vesicular membrane fusion and synaptic transmission. Thus, we suggest that NSF in this cluster would be the nearest gene responsible for the learning disability phenotype.

Molecular interaction network and pathway studies of ADAM33 potentially relevant to asthma

BACKGROUND

Asthma is a complex disease caused by gene-gene, gene-protein, and protein-protein interactions and the influence of environment, which plays a significant role in causing asthma pathogenesis. ADAM33 is known to be an important gene involved in asthma pathogenesis. No one single gene is a causal factor of asthma; rather, asthma is caused by a complex interaction of multiple genes having pathogenetic and protective effects.

OBJECTIVE

To identify and understand the interacting genes and proteins of ADAM33.

METHODS

The Ingenuity Pathway Analysis and GeneMANIA tools and a literature survey were used to identify the interacting candidates of ADAM33 and the WEB-based GEne SeT AnaLysis Toolkit was used to perform enrichment analysis of the proteins identified.

RESULTS

Keeping ADAM33 as a major hub, the authors identified some proteins whose interaction with ADAM33 had been associated with asthma and they recognized some proteins, such as amyloid β (A4) precursor protein, ataxin-7, α4-integrin, α5-integrin, α9-integrin, tissue inhibitor of metalloproteinase-4, and ubiquilin-4, that had not been previously associated with asthma.

CONCLUSION

The proteins identified in this study were enriched for various mechanisms that are involved in airway hyperresponsiveness, and through the interaction with ADAM33, they may have potential relevance in asthma.

Copy number variations burden on miRNA genes reveals layers of complexities involved in the regulation of pathways and phenotypic expression

MicroRNAs are involved in post-transcriptional down-regulation of gene expression. Variations in miRNA genes can severely affect downstream-regulated genes and their pathways. However, population-specific burden of CNVs on miRNA genes and the complexities created towards the phenotype is not known. From a total of 44109 CNVs investigated from 1715 individuals across 12 populations using high-throughput arrays, 4007 miRNA-CNVs (∼ 9%) consisting 6542 (∼ 5%) miRNA genes with a total of 333 (∼ 5%) singleton miRNA genes were identified. We found miRNA-CNVs across the genomes of individuals showing multiple hits in many targets, co-regulated under the same pathway. This study proposes four mechanisms unraveling the many complexities in miRNA genes, targets and co-regulated miRNA genes towards establishment of phenotypic diversity.

Genome-wide copy number scan identifies disruption of PCDH11X in developmental dyslexia

Developmental dyslexia (DD) is a complex heritable disorder with unexpected difficulty in learning to read and spell despite adequate intelligence, education, environment, and normal senses. We performed a whole genome copy number variations (CNV) scan on 11 dyslexic families consisting of 14 dyslexic subjects and 24 non dyslexic members using 1.8 million combined SNP and CNV markers. We found CNVs affecting protocadherin genes in six dyslexics from three families, while none among the non-dyslexic control members showed any CNV in protocadherins. We identified duplications in five cases and a deletion in one case in Xq21.3 region bearing PCDH11X. Unequal recombination between the X-transposed region (XTR) of Yp11.2 and the X chromosome might be causing these structural changes. PCDH11X, expressed in brain is implicated in cell-cell communication, verbal ability, cerebral asymmetry, and dendritic synaptic plasticity, may be regarded as a new candidate gene for dyslexia.

Mutation analysis of the SLC4A11 gene in Indian families with congenital hereditary endothelial dystrophy 2 and a review of the literature

PURPOSE

Congenital hereditary endothelial dystrophy 2 (CHED2) is an autosomal recessive disorder caused by mutations in the solute carrier family 4, sodium borate transporter, member 11 (SLC4A11) gene. The purpose of this study was to identify the genetic cause of CHED2 in six Indian families and catalog all known mutations in the SLC4A11 gene.

METHODS

Peripheral blood samples were collected from individuals of the families with CHED2 and used in genomic DNA isolation. PCR primers were used to amplify the entire coding region including intron-exon junctions of SLC4A11. Amplicons were subsequently sequenced to identify the mutations.

RESULTS

DNA sequence analysis of the six families identified four novel (viz., p.Thr262Ile, p.Gly417Arg, p.Cys611Arg, and p.His724Asp) mutations and one known p.Arg869His homozygous mutation in the SLC4A11 gene. The mutation p.Gly417Arg was identified in two families.

CONCLUSIONS

This study increases the mutation spectrum of the SLC4A11 gene. A review of the literature showed that the total number of mutations in the SLC4A11 gene described to date is 78. Most of the mutations are missense, followed by insertions-deletions. The present study will be helpful in genetic diagnosis of the families reported here.

Unravelling the complexity of human olfactory receptor repertoire by copy number analysis across population using high resolution arrays

Olfactory receptors (OR), responsible for detection of odor molecules, belong to the largest family of genes and are highly polymorphic in nature having distinct polymorphisms associated with specific regions around the globe. Since there are no reports on the presence of copy number variations in OR repertoire of Indian population, the present investigation in 43 Indians along with 270 HapMap and 31 Tibetan samples was undertaken to study genome variability and evolution. Analysis was performed using Affymetrix Genome-Wide Human SNP Array 6.0 chip, Affymterix CytoScan^® High-Density array, HD-CNV, and MAFFT program. We observed a total of 1527 OR genes in 503 CNV events from 81.3% of the study group, which includes 67.6% duplications and 32.4% deletions encompassing more of genes than pseudogenes. We report human genotypic variation in functional OR repertoire size across populations and it was found that the combinatorial effect of both “orthologous obtained from closely related species” and “paralogous derived sequences” provide the complexity to the continuously occurring OR CNVs.

Copy number variation-based polymorphism in a new pseudoautosomal region 3 (PAR3) of a human X-chromosome-transposed region (XTR) in the Y chromosome

A 3.5-Mb region of the X chromosome underwent duplication and transposition to the Y chromosome ~5-6 Mya. This X-transposed-region (XTR) originated at Xq21.3 and was inserted at Yp11.2. The two locations have 98.78 % homology and a high concentration of tandem repeats. In whole-genome scans of ten large families with dyslexic members, we identified transposed blocks comprising >102 kb of the Yp11.2 region in its homologous region at Xq21.3 in three females from three different families. Although recombination is known to be limited only to the pseudoautosomal regions (PARs) of the X and Y chromosomes, we report allelic unequal recombination between the XTR region Yp11.2 and Xq21.3, indicating the presence of a new PAR, which we named PAR3. This PAR3 region was also found in 2 % of the general population. An additional layer of justification could be provided from six other dyslexic cases which harbored duplications and deletions in the same Xq21.3 and Yp11.2 regions through allelic unequal recombination.

Family-based genome-wide copy number scan identifies five new genes of dyslexia involved in dendritic spinal plasticity

Genome-wide screening for copy number variations (CNVs) in ten Indian dyslexic families revealed the presence of five de novo CNVs in regions harboring GABARAP, NEGR1, ACCN1, DCDC5, and one in already known candidate gene CNTNAP2. These genes are located on regions of chromosomes 17p13.1, 1p31.1, 17q11.21, 11p14.1 and 7q35, respectively, and are implicated in learning, cognition and memory processes through dendritic spinal plasticity, though not formally associated with dyslexia. Molecular network analysis of these and other dyslexia-related module genes suggests them to be associated with synaptic transmission, axon guidance and cell adhesion. Thus, we suggest that dyslexia may also be caused by neuronal disconnection in addition to the earlier view that it is due to neuronal migrational disorder.