Intronic Single Nucleotide Variants Research Articles

Novel characterization of Alzheimer’s disease genetic loci using long‐read sequencing

AbstractBackgroundAlzheimer’s disease (AD) is up to 60‐80% heritable, but less than ∼20% is explained by studies analyzing single nucleotide variants (SNVs). One limitation of short‐read whole‐genome sequencing (SRS) is the standard read length of 150 base pairs, which does not enable the detection of longer structural variants (SVs). Here we sequenced individuals using long‐read sequencing (LRS), which can sequence reads with an average length of ∼20 kilobases, allowing us to identify SVs previously uncaptured.MethodAll participants underwent whole‐genome LRS (∼15x coverage) and a subgroup (84%) underwent SRS. Out of 576 participants (47% males, age = 70.6±7.9 y.o.), 115 were diagnosed with AD or mild cognitive impairment, 365 were healthy controls, and 96 were diagnosed with a synucleinopathy (either Parkinson or Lewy Body disease). Eighty‐three index SNVs from loci associated with AD risk through GWAS (Bellenguez et al., Nature Genetics 2022) were genotyped with 30x coverage SRS, in addition to APOE2‐4. A 1Mbp window was defined around these SNVs to construct the discovery range for SVs (Sniffles2 population mode). Linkage disequilibrium (LD) was assessed between SNVs and SVs (CubeX).ResultA total of 14854 SVs were found across the AD risk loci (Figure1). After LD calculation, N = 197 SVs had a R2>0.1 (Figure2). The SVs with the highest LD (R2>0.7) are reported in Table1, among which there is a 322 bp deletion in the 3’ UTR region of the TMEM106B in high LD (R2 = 0.918) with the intronic SNV rs13237518. This TMEM106B locus has been previously associated with the risk of frontotemporal lobar dementia with TDP‐43 pathology in addition to AD, but the causative SNV has not been identified yet. This large deletion may mediate TMEM106B’s risk‐modulating role in AD and FTLD‐TDP (Chemparathy et al. medRxiv 2023). At the complex MAPT locus, three SVs showed a high LD with rs199515.ConclusionInsights into the role of SVs in neurodegenerative disorders have been hampered due to limitations with SRS. Using LRS in a large AD‐related sample, we characterized for the first time the genetic variation of SVs in known AD risk loci and provide a roadmap to identify potential causal SVs driving the AD association signal.

Short-read whole genome sequencing identifies causative variants in most individuals with previously unexplained aniridia

BackgroundClassic aniridia is a highly penetrant autosomal dominant disorder characterised by congenital absence of the iris, foveal hypoplasia, optic disc anomalies and progressive opacification of the cornea. >90% of cases...

Network science approach elucidates integrative genomic-metabolomic signature of antidepressant response and lifetime history of attempted suicide in adults with major depressive disorder.

Background: Individuals with major depressive disorder (MDD) and a lifetime history of attempted suicide demonstrate lower antidepressant response rates than those without a prior suicide attempt. Identifying biomarkers of antidepressant response and lifetime history of attempted suicide may help augment pharmacotherapy selection and improve the objectivity of suicide risk assessments. Towards this goal, this study sought to use network science approaches to establish a multi-omics (genomic and metabolomic) signature of antidepressant response and lifetime history of attempted suicide in adults with MDD. Methods: Single nucleotide variants (SNVs) which associated with suicide attempt(s) in the literature were identified and then integrated with a) p180-assayed metabolites collected prior to antidepressant pharmacotherapy and b) a binary measure of antidepressant response at 8 weeks of treatment using penalized regression-based networks in 245 ‘Pharmacogenomics Research Network Antidepressant Medication Study (PGRN-AMPS)’ and 103 ‘Combining Medications to Enhance Depression Outcomes (CO-MED)’ patients with major depressive disorder. This approach enabled characterization and comparison of biological profiles and associated antidepressant treatment outcomes of those with (N = 46) and without (N = 302) a self-reported lifetime history of suicide attempt. Results: 351 SNVs were associated with suicide attempt(s) in the literature. Intronic SNVs in the circadian genes CLOCK and ARNTL (encoding the CLOCK:BMAL1 heterodimer) were amongst the top network analysis features to differentiate patients with and without a prior suicide attempt. CLOCK and ARNTL differed in their correlations with plasma phosphatidylcholines, kynurenine, amino acids, and carnitines between groups. CLOCK and ARNTL-associated phosphatidylcholines showed a positive correlation with antidepressant response in individuals without a prior suicide attempt which was not observed in the group with a prior suicide attempt. Conclusion: Results provide evidence for a disturbance between CLOCK:BMAL1 circadian processes and circulating phosphatidylcholines, kynurenine, amino acids, and carnitines in individuals with MDD who have attempted suicide. This disturbance may provide mechanistic insights for differential antidepressant pharmacotherapy outcomes between patients with MDD with versus without a lifetime history of attempted suicide. Future investigations of CLOCK:BMAL1 metabolic regulation in the context of suicide attempts may help move towards biologically-augmented pharmacotherapy selection and stratification of suicide risk for subgroups of patients with MDD and a lifetime history of attempted suicide.

A common intronic single nucleotide variant modifies PKD1 expression level.

Autosomal dominant polycystic kidney disease (ADPKD), caused by mutations in PKD1 and PKD2 (PKD1/2), has unexplained phenotypic variability likely affected by environmental and other genetic factors. Approximately 10% of individuals with ADPKD phenotype have no causal mutation detected, possibly due to unrecognized risk variants of PKD1/2. This study was designed to identify risk variants of PKD genes through population genetic analyses. We used Wright's F-statistics (Fst) to evaluate common single nucleotide variants (SNVs) potentially favored by positive natural selection in PKD1 from 1000 Genomes Project (1KG) and genotyped 388 subjects from the Rogosin Institute ADPKD Data Repository. The variants with >90th percentile Fst scores underwent further investigation by in silico analysis and molecular genetics analyses. We identified a deep intronic SNV, rs3874648G> A, located in a conserved binding site of the splicing regulator Tra2-β in PKD1 intron 30. Reverse-transcription PCR (RT-PCR) of peripheral blood leukocytes (PBL) from an ADPKD patient homozygous for rs3874648-A identified an atypical PKD1 splice form. Functional analyses demonstrated that rs3874648-A allele increased Tra2-β binding affinity and activated a cryptic acceptor splice-site, causing a frameshift that introduced a premature stop codon in mRNA, thereby decreasing PKD1 full-length transcript level. PKD1 transcript levels were lower in PBL from rs3874648-G/A carriers than in rs3874648-G/G homozygotes in a small cohort of normal individuals and patients with PKD2 inactivating mutations. Our findings indicate that rs3874648G > A is a PKD1 expression modifier attenuating PKD1 expression through Tra2-β, while the derived G allele advantageously maintains PKD1 expression and is predominant in all subpopulations.

RNA-seq analysis, targeted long-read sequencing and in silico prediction to unravel pathogenic intronic events and complicated splicing abnormalities in dystrophinopathy.

Dystrophinopathy is caused by alterations in DMD. Approximately 1% of patients remain genetically undiagnosed, because intronic variations are not detected by standard methods. Here, we combined laboratory and in silico analyses to identify disease-causing genomic variants in genetically undiagnosed patients and determine the regulatory mechanisms underlying abnormal DMD transcript generation. DMD transcripts from 20 genetically undiagnosed dystrophinopathy patients in whom no exon variants were identified, despite dystrophin deficiency on muscle biopsy, were analyzed by transcriptome sequencing. Genome sequencing captured intronic variants and their effects were interpreted using in silico tools. Targeted long-read sequencing was applied in cases with suspected structural genomic abnormalities. Abnormal DMD transcripts were detected in 19 of 20 cases; Exonization of intronic sequences in 15 cases, exon skipping in one case, aberrantly spliced and polyadenylated transcripts in two cases and transcription termination in one case. Intronic single nucleotide variants, chromosomal rearrangements and nucleotide repeat expansion were identified in DMD gene as pathogenic causes of transcript alteration. Our combined analysis approach successfully identified pathogenic events. Detection of diseasing-causing mechanisms in DMD transcripts could inform the therapeutic options for patients with dystrophinopathy.

Clinical impact of variants in non-coding regions of SHOX - Current knowledge.

The short stature homeobox-containing (SHOX) is the most frequently analysed gene in patients classified as short stature patients (ISS) or diagnosed with Leri-Weill dyschondrosteosis (LWD), Langer mesomelic dysplasia (LMD), or Madelung deformity (MD). However, clinical testing of this gene focuses primarily on single nucleotide variants (SNV) in its coding sequences and copy number variants (CNV) overlapping SHOX gene. This review summarizes the clinical impact of variants in noncoding regions of SHOX. RECENT FINDINGS: CNV extending exclusively into the regulatory elements (i.e., not interrupting the coding sequence) are found more frequently in downstream regulatory elements of SHOX. Further, duplications are more frequent than deletions. Interestingly, downstream duplications are more common than deletions in patients with ISS or LWD but no such differences exist for upstream CNV. Moreover, the presence of specific CNVs in the patient population suggests the involvement of additional unknown factors. Some of its intronic variants, notably NM_000451.3(SHOX):c.-9delG and c.-65C>A in the 5'UTR, have unclear clinical roles. However, these intronic SNV may increase the probability that other CNV will arise de novo in the SHOX gene based on homologous recombination or incorrect splicing of mRNA. SUMMARY: This review highlights the clinical impact of noncoding changes in the SHOX gene and the need to apply new technologies and genotype-phenotype correlation in their analysis.

WGS and RNA Studies Diagnose Noncoding DMD Variants in Males With High Creatine Kinase.

ObjectiveTo describe the diagnostic utility of whole-genome sequencing and RNA studies in boys with suspected dystrophinopathy, for whom multiplex ligation-dependent probe amplification and exomic parallel sequencing failed to yield a genetic diagnosis, and to use remnant normal DMD splicing in 3 families to define critical levels of wild-type dystrophin bridging clinical spectrums of Duchenne to myalgia.MethodsExome, genome, and/or muscle RNA sequencing was performed for 7 males with elevated creatine kinase. PCR of muscle-derived complementary DNA (cDNA) studied consequences for DMD premessenger RNA (pre-mRNA) splicing. Quantitative Western blot was used to determine levels of dystrophin, relative to control muscle.ResultsSplice-altering intronic single nucleotide variants or structural rearrangements in DMD were identified in all 7 families. Four individuals, with abnormal splicing causing a premature stop codon and nonsense-mediated decay, expressed remnant levels of normally spliced DMD mRNA. Quantitative Western blot enabled correlation of wild-type dystrophin and clinical severity, with 0%–5% dystrophin conferring a Duchenne phenotype, 10% ± 2% a Becker phenotype, and 15% ± 2% dystrophin associated with myalgia without manifesting weakness.ConclusionsWhole-genome sequencing relied heavily on RNA studies to identify DMD splice-altering variants. Short-read RNA sequencing was regularly confounded by the effectiveness of nonsense-mediated mRNA decay and low read depth of the giant DMD mRNA. PCR of muscle cDNA provided a simple, yet informative approach. Highly relevant to genetic therapies for dystrophinopathies, our data align strongly with previous studies of mutant dystrophin in Becker muscular dystrophy, with the collective conclusion that a fractional increase in levels of normal dystrophin between 5% and 20% is clinically significant.

Comprehensive characterisation of intronic mis-splicing mutations in human cancers

Previous studies studying mis-splicing mutations were based on exome data and thus our current knowledge is largely limited to exons and the canonical splice sites. To comprehensively characterise intronic mis-splicing mutations, we analysed 1134 pan-cancer whole genomes and transcriptomes together with 3022 normal control samples. The ratio-based splicing analysis resulted in 678 somatic intronic mutations, with 46% residing in deep introns. Among the 309 deep intronic single nucleotide variants, 245 altered core splicing codes, with 38% activating cryptic splice sites, 12% activating cryptic polypyrimidine tracts, and 36% and 12% disrupting authentic polypyrimidine tracts and branchpoints, respectively. All the intronic cryptic splice sites were created at pre-existing GT/AG dinucleotides or by GC-to-GT conversion. Notably, 85 deep intronic mutations indicated gain of splicing enhancers or loss of splicing silencers. We found that 64 tumour suppressors were affected by intronic mutations and blood cancers showed higher proportion of deep intronic mutations. In particular, a telomere maintenance gene, POT1, was recurrently mis-spliced by deep intronic mutations in blood cancers. We validated a pseudoexon activation involving a splicing silencer in POT1 by CRISPR/Cas9. Our results shed light on previously unappreciated mechanisms by which noncoding mutations acting on splicing codes in deep introns contribute to tumourigenesis.

Cryptic exon activation causes dystrophinopathy in two Chinese families.

The X-linked recessive degenerative disease dystrophinopathy results from variants in the DMD gene. Given the large size and complexity of the DMD gene, molecular diagnosis for all dystrophinopathies remains challenging. Here we identified two cryptic exon retention variants caused by intronic single nucleotide variants in dystrophinopathy patients using combined RNA- and DNA-based methods. As one variant was previously unreported, we explored its likely pathogenic mechanism, via bioinformatic prediction for in silico verification of splicing. Then we constructed a minigene system harboring the variant and used morpholino modified antisense oligonucleotides (ASOs) to induce cryptic exon skipping. ASOs treatment corrected the mis-splicing in the mutant minigene system. Our study defines a novel intronic variant that can cause dystrophinopathy, and illustrates a strategy to overcome the aberrant splicing.

RegSNPs-intron: a computational framework for predicting pathogenic impact of intronic single nucleotide variants

Single nucleotide variants (SNVs) in intronic regions have yet to be systematically investigated for their disease-causing potential. Using known pathogenic and neutral intronic SNVs (iSNVs) as training data, we develop the RegSNPs-intron algorithm based on a random forest classifier that integrates RNA splicing, protein structure, and evolutionary conservation features. RegSNPs-intron showed excellent performance in evaluating the pathogenic impacts of iSNVs. Using a high-throughput functional reporter assay called ASSET-seq (ASsay for Splicing using ExonTrap and sequencing), we evaluate the impact of RegSNPs-intron predictions on splicing outcome. Together, RegSNPs-intron and ASSET-seq enable effective prioritization of iSNVs for disease pathogenesis.

RNA Splicing Defects in Cancer-Linked Genes Indicate Mutation or Focal Gene Deletion and Are Associated with TKI Resistance in CML

Background Mutated cancer genes in patients (pts) with TKI failure and blast crisis (BC) CML have recently been described. RUNX1 mutations, namely single nucleotide variants (SNVs) and indels, were the most frequently detected besides BCR-ABL1 [reviewed in Branford, Kim Leuk 2019]. They were found in ~18% of pts, although splice variants were rarely described. RNA splicing events were associated with focal deletion of IKZF1 and RUNX1 in TKI resistant pts that were identified by copy number analysis and RNAseq [Branford Blood 2018]. Novel splicing associated with mutation of cancer genes is an unexplored area of study in resistance. RNA sequencing can assess the functional effect of splice site variants, which lead to splicing errors due to the use of alternative or cryptic splice sites and cause alterations to protein function. Aim We determined whether novel splicing can identify cancer genes with potential altered function. Methods RNAseq analysis was performed for 48 pts at diagnosis and 33 at BC using a protocol that preserved intron-retaining precursor RNA. Coverage of intron-exon borders was sufficient to detect intronic splice region variants. The STAR aligner was used to bioinformatically collate unannotated RNA splice junctions. 54 cancer genes were assessed and aberrant splice events were filtered based on the number of samples in which a splice junction occurred. Manual inspection of the splice junctions was performed using the Integrative Genomics Viewer. This approach identified previously verified aberrant splicing associated with IKZF1 and RUNX1 deletions. Results Ten previously undetected novel splice junctions were revealed in 9/33 pts (27%) in BC within key tumor suppressor genes CDKN2A/B (5), RB1 (1), ATM (1), and RUNX1 (3). The aberrant splicing pattern of CDKN2A and RB1 (Fig A/B) in 6 pts suggested large deletions, as previously described in our cohort with IKZF1 and RUNX1 deletions. Breakpoints associated with deletions ranging from 53 to 181 Kb were detected in the 5 pts with CDKN2A aberrant splicing. Similarly, a 90 Kb deletion of exons 18-27 of the RB1 gene led to the aberrant splicing. The pts transformed to lymphoid BC (median 5 months). 4 of these 6 pts were tested at diagnosis and the deletions were not detected, indicating they were gained at resistance. The aberrant splicing patterns of ATM and RUNX1 did not predict large deletions. These were related to somatic SNVs at canonical splice sites in ATM and in 2 of the pts with RUNX1 aberrant splicing. A splice acceptor site SNV in ATM resulted in skipping of exon 61 (Fig C) and protein truncation. This novel SNV has not been reported in any population or somatic variant database. Two pts in myeloid BC at 28 and 48 months after diagnosis had an identical somatic RUNX1 mutation at the canonical splice donor site of exon 5. The SNV was not detectable prior to imatinib treatment in both pts. The splice site SNV led to activation of a cryptic splice site within exon 5 in both pts (Fig D), which predicted premature termination. While this mutation is novel, an adjacent intronic SNV occurs in familial platelet disorder, leading to activation of the same cryptic splice site. The atypical RUNX1 splicing of the 3rd patient was associated with retention of 55 bp of intron 6 as a cryptic exon (Fig E), leading to protein truncation. A deep intronic SNV identified at lymphoid BC at 6 months of imatinib was detected near the cryptic exon by RNAseq and verified as somatic by DNA Sanger sequencing. This was predicted to activate cryptic RNA splicing elements and lead to intron sequence retention in a RUNX1 transcript. We sequenced the diagnosis sample using an RNA-based gene panel method under development that provides enhanced sensitivity of variant detection. The same pattern of atypical splicing was observed and the intronic SNV was present at low level. The RUNX1 mutation at diagnosis may have contributed to early BC. To our knowledge this is the first report of a RUNX1 truncating variant in CML involving a cryptic exon. Conclusion Enhanced bioinformatic analysis of RNAseq data has revealed a high proportion of pts with truncating mutations in cancer genes indicated by novel RNA splicing (27% pts in BC). Using RNA-based sequencing allows an evaluation of the potential functional effect of variants that are not apparent by DNA-based mutation analysis. We suggest that future studies include RNA sequencing to detect a broader spectrum of mutations associated with TKI resistance. Disclosures Shanmuganathan: Gilead: Other: Travel Support; Janssen: Other: Travel Support; Amgen: Other: Travel Support; Bristol-Myers Squibb: Honoraria, Other: Travel Support; Novartis: Honoraria, Other: Travel Support. Yeung:Novartis: Honoraria, Research Funding; BMS: Honoraria, Research Funding; Pfizer: Honoraria; Amgen: Honoraria. Scott:Celgene: Honoraria. Hughes:Novartis, Bristol-Myers Squibb, Celgene: Research Funding; Novartis, Bristol-Myers Squibb: Consultancy, Other: Travel. Branford:Cepheid: Consultancy, Honoraria; Qiagen: Consultancy, Honoraria; Novartis: Consultancy, Honoraria, Research Funding, Speakers Bureau; Bristol-Myers Squibb: Honoraria, Speakers Bureau.

Validation of a Customized Bioinformatics Pipeline for a Clinical Next-Generation Sequencing Test Targeting Solid Tumor–Associated Variants

Bioinformatic analysis is an integral and critical part of clinical next-generation sequencing. It is especially challenging for some pipelines to consistently identify insertions and deletions. We present the validation of an open source tumor amplicon pipeline (OTA-pipeline) for clinical next-generation sequencing targeting solid tumor-associated variants. Raw data generated from 557 TruSight Tumor 26 samples and in silico data were analyzed by the OTA-pipeline and legacy pipeline and compared. Discrepant results were confirmed by orthogonal methods. The OTA-pipeline reported 22 variants that were not detected by the previously validated pipeline, including seven synonymous or intronic single-nucleotide variants, five single-nucleotide variants at frequency <5%, one insertion, and nine deletions. Variant allele frequencies reported by the two pipelines were highly concordant, although a few significant discrepancies were present. Analysis of in silico FASTQ files demonstrated a higher sensitivity of detecting complex insertions and deletions with the OTA-pipeline. The higher sensitivity came at a cost, because false-positive calls were increased in difficult-to-sequence regions. However, these calls were all flagged by our strand bias filter, distinguishing them from true variants. Our validation process provides a model for laboratories that want to establish an in-house bioinformatics pipeline for clinical next-generation sequencing.

Whole genome sequencing of an African American family highlights toll like receptor 6 variants in Kawasaki disease susceptibility.

Kawasaki disease (KD) is the most common acquired pediatric heart disease. We analyzed Whole Genome Sequences (WGS) from a 6-member African American family in which KD affected two of four children. We sought rare, potentially causative genotypes by sequentially applying the following WGS filters: sequence quality scores, inheritance model (recessive homozygous and compound heterozygous), predicted deleteriousness, allele frequency, genes in KD-associated pathways or with significant associations in published KD genome-wide association studies (GWAS), and with differential expression in KD blood transcriptomes. Biologically plausible genotypes were identified in twelve variants in six genes in the two affected children. The affected siblings were compound heterozygous for the rare variants p.Leu194Pro and p.Arg247Lys in Toll-like receptor 6 (TLR6), which affect TLR6 signaling. The affected children were also homozygous for three common, linked (r2 = 1) intronic single nucleotide variants (SNVs) in TLR6 (rs56245262, rs56083757 and rs7669329), that have previously shown association with KD in cohorts of European descent. Using transcriptome data from pre-treatment whole blood of KD subjects (n = 146), expression quantitative trait loci (eQTL) analyses were performed. Subjects homozygous for the intronic risk allele (A allele of TLR6 rs56245262) had differential expression of Interleukin-6 (IL-6) as a function of genotype (p = 0.0007) and a higher erythrocyte sedimentation rate at diagnosis. TLR6 plays an important role in pathogen-associated molecular pattern recognition, and sequence variations may affect binding affinities that in turn influence KD susceptibility. This integrative genomic approach illustrates how the analysis of WGS in multiplex families with a complex genetic disease allows examination of both the common disease–common variant and common disease–rare variant hypotheses.

Non-coding single nucleotide variants affecting estrogen receptor binding and activity.

BackgroundEstrogen receptor (ER) activity is critical for the development and progression of the majority of breast cancers. It is known that ER is differentially bound to DNA leading to transcriptomic and phenotypic changes in different breast cancer models. We investigated whether single nucleotide variants (SNVs) in ER binding sites (regSNVs) contribute to ER action through changes in the ER cistrome, thereby affecting disease progression. Here we developed a computational pipeline to identify SNVs in ER binding sites using chromatin immunoprecipitation sequencing (ChIP-seq) data from ER+ breast cancer models.MethodsER ChIP-seq data were downloaded from the Gene Expression Omnibus (GEO). GATK pipeline was used to identify SNVs and the MACS algorithm was employed to call DNA-binding sites. Determination of the potential effect of a given SNV in a binding site was inferred using reimplementation of the is-rSNP algorithm. The Cancer Genome Atlas (TCGA) data were integrated to correlate the regSNVs and gene expression in breast tumors. ChIP and luciferase assays were used to assess the allele-specific binding.ResultsAnalysis of ER ChIP-seq data from MCF7 cells identified an intronic SNV in the IGF1R gene, rs62022087, predicted to increase ER binding. Functional studies confirmed that ER binds preferentially to rs62022087 versus the wild-type allele. By integrating 43 ER ChIP-seq datasets, multi-omics, and clinical data, we identified 17 regSNVs associated with altered expression of adjacent genes in ER+ disease. Of these, the top candidate was in the promoter of the GSTM1 gene and was associated with higher expression of GSTM1 in breast tumors. Survival analysis of patients with ER+ tumors revealed that higher expression of GSTM1, responsible for detoxifying carcinogens, was correlated with better outcome.ConclusionsIn conclusion, we have developed a computational approach that is capable of identifying putative regSNVs in ER ChIP-binding sites. These non-coding variants could potentially regulate target genes and may contribute to clinical prognosis in breast cancer.Electronic supplementary materialThe online version of this article (doi:10.1186/s13073-016-0382-0) contains supplementary material, which is available to authorized users.

P6012 Use of targeted next generation re-sequencing in the identification of polymorphisms in the bovine collagenous lectin gene family

Collagenous lectins bind carbohydrate motifs on pathogens, leading either to the activation of the lectin complement pathway or to the opsonization or agglutination of pathogens. They play an important role in innate immunity against a variety of bacteria, viruses, and fungi. Functionally altered proteins resulting from genetic mutations in collagenous lectins have been shown in other species to predispose animals to infectious disease. This study aimed to 1) identify genetic variation in the bovine collagenous lectin genes; and 2) determine whether polymorphisms were associated with an increased susceptibility to infectious disease. We used pooled, targeted next generation re-sequencing to identify variants in the bovine collagenous lectin genes. Cattle submitted for post-mortem examination at the University of Guelph were classified as normal (n = 40) or diseased (n = 80) based on the presence or absence of infectious disease. Cattle were placed into groups of 5 based on the similarity of diagnosis, and an equal amount of DNA from each animal was pooled. The collagenous lectin genes (including three unique to bovids) along with 3 kb of downstream DNA and up to 50 kb of upstream DNA were targeted for re-sequencing. The sequencing library was prepared with a Roche Nimblegen EZ Developer kit and sequenced on an Illumina MiSeq. In total, 4.6 Gb of usable sequence data was obtained with an average read depth of 42x/cow over the target region. Following application of quality control filters, 6525 single nucleotide variants (SNVs) were found, including 510 not reported in dbSNP. This included 3948 upstream region SNVs, 2672 downstream region SNVs, and 411 intronic SNVs. Within exons, 107 SNVs, including 54 missense mutations, were identified. In silico analysis of the missense mutations identified 16 SNVs with significant potentially disruptive effects on protein structure. A mutation in MBL2, resulting in a P42Q change in the collagen-like domain, holds particular interest, as similar mutations in orthologous genes have been shown to have impact on susceptibility to disease. Allele frequencies between the normal and diseased populations were compared and the potential impact of promoter SNVs investigated. This study demonstrates that pooled, targeted re-sequencing is a cost effective method of polymorphism identification and discovery in cattle. We identified 510 previously unreported SNVs, as well as 16 mutations potentially affecting collagenous lectin structure or function. These SNVs will help in our understanding of the genetics of disease susceptibility, and represent potential candidates for genetic selection.

Identification and Functional Studies of Regulatory Variants Responsible for the Association of NRG3 with a Delusion Phenotype in Schizophrenia

We previously reported a genetic linkage for schizophrenia (SZ; nonparametric linkage score of 4.27) at 10q22 in an Ashkenazi Jewish (AJ) population. In follow-up fine-mapping, we found strong evidence for an association between 3 intronic single nucleotide variants (SNVs) in the 5′ end of neuregulin 3 (NRG3) and the delusion factor score of our phenotypic principal component analysis. Two independent groups replicated these findings, indicating that variants in NRG3 confer a risk for a delusion-rich SZ subtype. To identify the causative variants, we sequenced the 162-kb linkage disequilibrium block covering the NRG3 5′ end in 47 AJ SZ patients at the extremes of the delusion factor quantitative trait distribution. Among the identified variants, we found 5 noncoding SNVs which were present on the high delusion factor haplotype and significantly overrepresented in high delusion factor subjects. We tested these for regulatory effects and found that risk alleles of rs10883866 and rs60827755 decreased and increased, respectively, the expression of a reporter gene as compared to the reference allele. In postmortem brain mRNA quantification experiments, we found the same variants also perturb the relative expression of alternative NRG3 isoforms. In summary, we have identified regulatory SNVs contributing to the association of NRG3 with delusion symptoms in SZ.