Publications by authors named "Mehdi Zarrei"

34 Publications

Copy number variations in a Brazilian cohort with autism spectrum disorders highlight the contribution of cell adhesion genes.

Clin Genet 2021 Oct 19. Epub 2021 Oct 19.

Departamento de Genética e Biologia Evolutiva, Centro de Estudos do Genoma Humano e Células-tronco, Instituto de Biociências, Universidade de São Paulo, São Paulo, SP, Brazil.

Prediction of pathogenicity of rare copy number variations (CNVs), a genomic alteration known to contribute to the etiology of autism spectrum disorder (ASD), represents a serious limitation to interpreting genetic tests, particularly for genetic counseling purposes. Chromosomal microarray analysis (CMA) was conducted in a unique collection of 144 Brazilian individuals with ASD of strong European and African ancestries. Rare CNVs were detected in 39 patients: 41 of unknown significance (VUS), four pathogenic and one likely pathogenic CNVs (clinical yield of 4.1%; 5/122). Based on gene content and recurrence in three large cohorts [a Brazilian neurodevelopmental disorder cohort, the autism MSSNG cohort, and the Canadian-based Centre for Applied Genomics microarray database], this work strengthened the pathogenicity of 14 genes (FAT1, CAMK4, BIRC6, DPP6, CSMD1, CTNNA3, CDH8/CDH11, CDH13, OR1C1, CNTN6, CNTNAP4, FGF2 and PTPRN2) within 14 CNVs. Notably, enrichment of cell adhesion proteins to ASD etiology was identified (p < 0.05), highlighting the importance of these gene families in the etiology of ASD.
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http://dx.doi.org/10.1111/cge.14072DOI Listing
October 2021

Inherited duplications of PPP2R3B predispose to nevi and melanoma via a C21orf91-driven proliferative phenotype.

Genet Med 2021 09 18;23(9):1636-1647. Epub 2021 Jun 18.

Department of Twin Research and Genetic Epidemiology, King's College London, South Wing Block D, London, UK.

Purpose: Much of the heredity of melanoma remains unexplained. We sought predisposing germline copy-number variants using a rare disease approach.

Methods: Whole-genome copy-number findings in patients with melanoma predisposition syndrome congenital melanocytic nevus were extrapolated to a sporadic melanoma cohort. Functional effects of duplications in PPP2R3B were investigated using immunohistochemistry, transcriptomics, and stable inducible cellular models, themselves characterized using RNAseq, quantitative real-time polymerase chain reaction (qRT-PCR), reverse phase protein arrays, immunoblotting, RNA interference, immunocytochemistry, proliferation, and migration assays.

Results: We identify here a previously unreported genetic susceptibility to melanoma and melanocytic nevi, familial duplications of gene PPP2R3B. This encodes PR70, a regulatory unit of critical phosphatase PP2A. Duplications increase expression of PR70 in human nevus, and increased expression in melanoma tissue correlates with survival via a nonimmunological mechanism. PPP2R3B overexpression induces pigment cell switching toward proliferation and away from migration. Importantly, this is independent of the known microphthalmia-associated transcription factor (MITF)-controlled switch, instead driven by C21orf91. Finally, C21orf91 is demonstrated to be downstream of MITF as well as PR70.

Conclusion: This work confirms the power of a rare disease approach, identifying a previously unreported copy-number change predisposing to melanocytic neoplasia, and discovers C21orf91 as a potentially targetable hub in the control of phenotype switching.
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http://dx.doi.org/10.1038/s41436-021-01204-yDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8460442PMC
September 2021

RCL1 copy number variants are associated with a range of neuropsychiatric phenotypes.

Mol Psychiatry 2021 05 17;26(5):1706-1718. Epub 2021 Feb 17.

The Manton Center for Orphan Disease Research, Boston Children's Hospital, Boston, MA, USA.

Mendelian and early-onset severe psychiatric phenotypes often involve genetic variants having a large effect, offering opportunities for genetic discoveries and early therapeutic interventions. Here, the index case is an 18-year-old boy, who at 14 years of age had a decline in cognitive functioning over the course of a year and subsequently presented with catatonia, auditory and visual hallucinations, paranoia, aggression, mood dysregulation, and disorganized thoughts. Exome sequencing revealed a stop-gain mutation in RCL1 (NM_005772.4:c.370 C > T, p.Gln124Ter), encoding an RNA 3'-terminal phosphate cyclase-like protein that is highly conserved across eukaryotic species. Subsequent investigations across two academic medical centers identified eleven additional cases of RCL1 copy number variations (CNVs) with varying neurodevelopmental or psychiatric phenotypes. These findings suggest that dosage variation of RCL1 contributes to a range of neurological and clinical phenotypes.
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http://dx.doi.org/10.1038/s41380-021-01035-yDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8159744PMC
May 2021

Genes and Pathways Implicated in Tetralogy of Fallot Revealed by Ultra-Rare Variant Burden Analysis in 231 Genome Sequences.

Front Genet 2020 15;11:957. Epub 2020 Sep 15.

Clinical Genetics Research Program, Centre for Addiction and Mental Health, Toronto, ON, Canada.

Recent genome-wide studies of rare genetic variants have begun to implicate novel mechanisms for tetralogy of Fallot (TOF), a severe congenital heart defect (CHD). To provide statistical support for case-only data without parental genomes, we re-analyzed genome sequences of 231 individuals with TOF ( = 175) or related CHD. We adapted a burden test originally developed for variants to assess ultra-rare variant burden in individual genes, and in gene-sets corresponding to functional pathways and mouse phenotypes, accounting for highly correlated gene-sets and for multiple testing. For truncating variants, the gene burden test confirmed significant burden in (Bonferroni corrected -value < 0.01). For missense variants, burden in achieved genome-wide significance only when restricted to constrained genes (i.e., under negative selection, Bonferroni corrected -value = 0.004), and showed enrichment for variants affecting the extracellular domain, especially those disrupting cysteine residues forming disulfide bonds (OR = 39.8 vs. gnomAD). Individuals with ultra-rare missense variants, all with TOF, were enriched for positive family history of CHD. Other genes not previously implicated in CHD had more modest statistical support in gene burden tests. Gene-set burden tests for truncating variants identified a cluster of pathways corresponding to VEGF signaling ( = 0%), and of mouse phenotypes corresponding to abnormal vasculature ( = 0.8%); these suggested additional candidate genes not previously identified (e.g., and ). Results for the most promising genes were driven by the TOF subset of the cohort. The findings support the importance of ultra-rare variants disrupting genes involved in VEGF and NOTCH signaling in the genetic architecture of TOF, accounting for 11-14% of individuals in the TOF cohort. These proof-of-principle data indicate that this statistical methodology could assist in analyzing case-only sequencing data in which ultra-rare variants, whether or inherited, contribute to the genetic etiopathogenesis of a complex disorder.
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http://dx.doi.org/10.3389/fgene.2020.00957DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7522597PMC
September 2020

Ancestry and frequency of genetic variants in the general population are confounders in the characterization of germline variants linked to cancer.

BMC Med Genet 2020 05 6;21(1):92. Epub 2020 May 6.

Charbonneau Cancer Institute, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada.

Background: Pediatric high-grade gliomas (pHGGs) are incurable malignant brain cancers. Clear somatic genetic drivers are difficult to identify in the majority of cases. We hypothesized that this may be due to the existence of germline variants that influence tumor etiology and/or progression and are filtered out using traditional pipelines for somatic mutation calling.

Methods: In this study, we analyzed whole-genome sequencing (WGS) datasets of matched germlines and tumor tissues to identify recurrent germline variants in pHGG patients.

Results: We identified two structural variants that were highly recurrent in a discovery cohort of 8 pHGG patients. One was a ~ 40 kb deletion immediately upstream of the NEGR1 locus and predicted to remove the promoter region of this gene. This copy number variant (CNV) was present in all patients in our discovery cohort (n = 8) and in 86.3% of patients in our validation cohort (n = 73 cases). We also identified a second recurrent deletion 55.7 kb in size affecting the BTNL3 and BTNL8 loci. This BTNL3-8 deletion was observed in 62.5% patients in our discovery cohort, and in 17.8% of the patients in the validation cohort. Our single-cell RNA sequencing (scRNA-seq) data showed that both deletions result in disruption of transcription of the affected genes. However, analysis of genomic information from multiple non-cancer cohorts showed that both the NEGR1 promoter deletion and the BTNL3-8 deletion were CNVs occurring at high frequencies in the general population. Intriguingly, the upstream NEGR1 CNV deletion was homozygous in ~ 40% of individuals in the non-cancer population. This finding was immediately relevant because the affected genes have important physiological functions, and our analyses showed that NEGR1 expression levels have prognostic value for pHGG patient survival. We also found that these deletions occurred at different frequencies among different ethnic groups.

Conclusions: Our study highlights the need to integrate cancer genomic analyses and genomic data from large control populations. Failure to do so may lead to spurious association of genes with cancer etiology. Importantly, our results showcase the need for careful evaluation of differences in the frequency of genetic variants among different ethnic groups.
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http://dx.doi.org/10.1186/s12881-020-01033-xDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7201963PMC
May 2020

Segregating patterns of copy number variations in extended autism spectrum disorder (ASD) pedigrees.

Am J Med Genet B Neuropsychiatr Genet 2020 07 6;183(5):268-276. Epub 2020 May 6.

Centre for Addiction and Mental Health, The Hospital for Sick Children & University of Toronto, Toronto, Ontario, Canada.

Autism spectrum disorder (ASD) is a relatively common childhood onset neurodevelopmental disorder with a complex genetic etiology. While progress has been made in identifying the de novo mutational landscape of ASD, the genetic factors that underpin the ASD's tendency to run in families are not well understood. In this study, nine extended pedigrees each with three or more individuals with ASD, and others with a lesser autism phenotype, were phenotyped and genotyped in an attempt to identify heritable copy number variants (CNVs). Although these families have previously generated linkage signals, no rare CNV segregated with these signals in any family. A small number of clinically relevant CNVs were identified. Only one CNV was identified that segregated with ASD phenotype; namely, a duplication overlapping DLGAP2 in three male offspring each with an ASD diagnosis. This gene encodes a synaptic scaffolding protein, part of a group of proteins known to be pathologically implicated in ASD. On the whole, however, the heritable nature of ASD in the families studied remains poorly understood.
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http://dx.doi.org/10.1002/ajmg.b.32785DOI Listing
July 2020

Refining critical regions in 15q24 microdeletion syndrome pertaining to autism.

Am J Med Genet B Neuropsychiatr Genet 2020 06 18;183(4):217-226. Epub 2020 Jan 18.

Pediatric Research Institute, Qilu Children's Hospital of Shandong University, Ji'nan, China.

Chromosome 15q24 microdeletion syndrome is characterized by developmental delay, facial dysmorphism, hearing loss, hypotonia, recurrent infection, and other congenital malformations including microcephaly, scoliosis, joint laxity, digital anomalies, as well as sometimes having autism spectrum disorder (ASD) and attention deficit hyperactivity disorder. Here, we report a boy with a 2.58-Mb de novo deletion at chromosome 15q24. He is diagnosed with ASD and having multiple phenotypes similar to those reported in cases having 15q24 microdeletion syndrome. To delineate the critical genes and region that might be responsible for these phenotypes, we reviewed all previously published cases. We observe a potential minimum critical region of 650 kb (LCR15q24A-B) affecting NEO1 among other genes that might pertinent to individuals with ASD carrying this deletion. In contrast, a previously defined minimum critical region downstream of the 650-kb interval (LCR15q24B-D) is more likely associated with the developmental delay, facial dysmorphism, recurrent infection, and other congenital malformations. As a result, the ASD phenotype in this individual is potentially attributed by genes particularly NEO1 within the newly proposed critical region.
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http://dx.doi.org/10.1002/ajmg.b.32778DOI Listing
June 2020

Meta-Analyses Support Previous and Novel Autism Candidate Genes: Outcomes of an Unexplored Brazilian Cohort.

Autism Res 2020 02 6;13(2):199-206. Epub 2019 Nov 6.

Departamento de Genética e Biologia Evolutiva, Centro de Estudos do Genoma Humano e Células-tronco, Instituto de Biociências, Universidade de São Paulo, São Paulo, SP, Brazil.

Large genomic databases of neurodevelopmental disorders (NDD) are helpful resources of genomic variations in complex and heterogeneous conditions, as Autism Spectrum Disorder (ASD). We evaluated the role of rare copy number variations (CNVs) and exonic de novo variants, in a molecularly unexplored Brazilian cohort of 30 ASD trios (n = 90), by performing a meta-analysis of our findings in more than 20,000 patients from NDD cohorts. We identified three pathogenic CNVs: two duplications on 1q21 and 17p13, and one deletion on 4q35. CNVs meta-analysis (n = 8,688 cases and n = 3,591 controls) confirmed 1q21 relevance by identifying duplications in other 16 ASD patients. Exome analysis led the identification of seven de novo variants in ASD genes (SFARI list): three loss-of-function pathogenic variants in CUL3, CACNA1H, and SHANK3; one missense pathogenic variant in KCNB1; and three deleterious missense variants in ATP10A, ANKS1B, and DOCK1. From the remaining 12 de novo variants in non-previous ASD genes, we prioritized PRPF8 and RBM14. Meta-analysis (n = 13,754 probands; n = 2,299 controls) identified six and two additional patients with validated de novo variants in PRPF8 and RBM14, respectively. By comparing the de novo variants with a previously established mutational rate model, PRPF8 showed nominal significance before multiple test correction (P = 0.039, P-value adjusted = 0.079, binomial test), suggesting its relevance to ASD. Approximately 60% of our patients presented comorbidities, and the diagnostic yield was estimated in 23% (7/30: three pathogenic CNVs and four pathogenic de novo variants). Our uncharacterized Brazilian cohort with tetra-hybrid ethnic composition was a valuable resource to validate and identify possible novel candidate loci. Autism Res 2020, 13: 199-206. © 2019 International Society for Autism Research, Wiley Periodicals, Inc. LAY SUMMARY: We believed that to study an unexplored autistic population, such as the Brazilian, could help to find novel genes for autism. In order to test this idea, with our limited budget, we compared candidate genes obtained from genomic analyses of 30 children and their parents, with those of more than 20,000 individuals from international studies. Happily, we identified a genetic cause in 23% of our patients and suggest a possible novel candidate gene for autism (PRPF8).
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http://dx.doi.org/10.1002/aur.2238DOI Listing
February 2020

A large data resource of genomic copy number variation across neurodevelopmental disorders.

NPJ Genom Med 2019 7;4:26. Epub 2019 Oct 7.

Hamilton Health Sciences, Ron Joyce Children's Health Centre, Hamilton, On Canada.

Copy number variations (CNVs) are implicated across many neurodevelopmental disorders (NDDs) and contribute to their shared genetic etiology. Multiple studies have attempted to identify shared etiology among NDDs, but this is the first genome-wide CNV analysis across autism spectrum disorder (ASD), attention deficit hyperactivity disorder (ADHD), schizophrenia (SCZ), and obsessive-compulsive disorder (OCD) at once. Using microarray (Affymetrix CytoScan HD), we genotyped 2,691 subjects diagnosed with an NDD (204 SCZ, 1,838 ASD, 427 ADHD and 222 OCD) and 1,769 family members, mainly parents. We identified rare CNVs, defined as those found in <0.1% of 10,851 population control samples. We found clinically relevant CNVs (broadly defined) in 284 (10.5%) of total subjects, including 22 (10.8%) among subjects with SCZ, 209 (11.4%) with ASD, 40 (9.4%) with ADHD, and 13 (5.6%) with OCD. Among all NDD subjects, we identified 17 (0.63%) with aneuploidies and 115 (4.3%) with known genomic disorder variants. We searched further for genes impacted by different CNVs in multiple disorders. Examples of NDD-associated genes linked across more than one disorder (listed in order of occurrence frequency) are , , , , , , , , , , and long non-coding RNAs: and . We demonstrated that CNVs impacting the same genes could potentially contribute to the etiology of multiple NDDs. The CNVs identified will serve as a useful resource for both research and diagnostic laboratories for prioritization of variants.
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http://dx.doi.org/10.1038/s41525-019-0098-3DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6779875PMC
October 2019

Expanding the neurodevelopmental phenotypes of individuals with de novo variants.

NPJ Genom Med 2019 26;4. Epub 2019 Apr 26.

1The Centre for Applied Genomics, Genetics and Genome Biology, The Hospital for Sick Children, Toronto, ON Canada.

De novo loss-of-function (LoF) variants in the gene are associated with Wiedemann-Steiner Syndrome (WSS). Recently, de novo variants have been identified in sequencing studies of cohorts of individuals with neurodevelopmental disorders (NDDs). However, most of these studies lack the detailed clinical information required to determine whether those individuals have isolated NDDs or WSS (i.e. syndromic NDDs). We performed thorough clinical and neurodevelopmental phenotyping on six individuals with de novo variants. From these data, we found that all six patients met clinical criteria for WSS and we further define the neurodevelopmental phenotypes associated with variants and WSS. In particular, we identified a subtype of Autism Spectrum Disorder (ASD) in five individuals, characterized by marked rigid, repetitive and inflexible behaviours, emotional dysregulation, externalizing behaviours, but relative social motivation. To further explore the clinical spectrum associated with variants, we also conducted a meta-analysis of individuals with variants reported in the published literature. We found that de novo LoF or missense variants in were significantly more prevalent than predicted by a previously established statistical model of de novo mutation rate for . Our genotype-phenotype findings better define the clinical spectrum associated with variants and suggest that individuals with de novo LoF and missense variants likely have a clinically unrecognized diagnosis of WSS, rather than isolated NDD or ASD alone. This highlights the importance of a clinical genetic and neurodevelopmental assessment for individuals with such variants in .
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http://dx.doi.org/10.1038/s41525-019-0083-xDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6486600PMC
April 2019

Intratumoral Genetic and Functional Heterogeneity in Pediatric Glioblastoma.

Cancer Res 2019 05 15;79(9):2111-2123. Epub 2019 Mar 15.

Department of Biochemistry and Molecular Biology, University of Calgary, Calgary, Alberta, Canada.

Pediatric glioblastoma (pGBM) is a lethal cancer with no effective therapies. To understand the mechanisms of tumor evolution in this cancer, we performed whole-genome sequencing with linked reads on longitudinally resected pGBM samples. Our analyses showed that all diagnostic and recurrent samples were collections of genetically diverse subclones. Clonal composition rapidly evolved at recurrence, with less than 8% of nonsynonymous single-nucleotide variants being shared in diagnostic-recurrent pairs. To track the origins of the mutational events observed in pGBM, we generated whole-genome datasets for two patients and their parents. These trios showed that genetic variants could be (i) somatic, (ii) inherited from a healthy parent, or (iii) in the germlines of pGBM patients. Analysis of variant allele frequencies supported a model of tumor growth involving slow-cycling cancer stem cells that give rise to fast-proliferating progenitor-like cells and to nondividing cells. Interestingly, radiation and antimitotic chemotherapeutics did not increase overall tumor burden upon recurrence. These findings support an important role for slow-cycling stem cell populations in contributing to recurrences, because slow-cycling cell populations are expected to be less prone to genotoxic stress induced by these treatments and therefore would accumulate few mutations. Our results highlight the need for new targeted treatments that account for the complex functional hierarchies and genomic heterogeneity of pGBM. SIGNIFICANCE: This work challenges several assumptions regarding the genetic organization of pediatric GBM and highlights mutagenic programs that start during early prenatal development. http://cancerres.aacrjournals.org/content/canres/79/9/2111/F1.large.jpg.
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http://dx.doi.org/10.1158/0008-5472.CAN-18-3441DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7282886PMC
May 2019

Rare copy number variation in extremely impulsively violent males.

Genes Brain Behav 2019 07 3;18(6):e12536. Epub 2018 Dec 3.

Research Unit for Rare Diseases, Department of Pediatrics and Adolescent Medicine, First Faculty of Medicine, Charles University, Prague, Czech Republic.

The genetic correlates of extreme impulsive violence are poorly understood, and there have been no studies that have systematically characterized a large group of affected individuals both clinically and genetically. We performed a genome-wide rare copy number variant (CNV) analysis in 281 males from four Czech prisons who met strict clinical criteria for extreme impulsive violence. Inclusion criteria included age ≥ 18 years, an ICD-10 diagnosis of Dissocial Personality Disorder, and the absence of an organic brain disorder. Participants underwent a structured psychiatric assessment to diagnose extreme impulsive violence and then provided a blood sample for genetic analysis. DNA was genotyped and CNVs were identified using Illumina HumanOmni2.5 single-nucleotide polymorphism array platform. Comparing with 10851 external population controls, we identified 828 rare CNVs (frequency ≤ 0.1% among control samples) in 264 participants. The CNVs impacted 754 genes, with 124 genes impacted more than once (2-25 times). Many of these genes are associated with autosomal dominant or X-linked disorders affecting adult behavior, cognition, learning, intelligence, specifically expressed in the brain and relevant to synapses, neurodevelopment, neurodegeneration, obesity and neuropsychiatric phenotypes. Specifically, we identified 31 CNVs of clinical relevance in 31 individuals, 59 likely clinically relevant CNVs in 49 individuals, and 17 recurrent CNVs in 65 individuals. Thus, 123 of 281 (44%) individuals had one to several rare CNVs that were indirectly or directly relevant to impulsive violence. Extreme impulsive violence is genetically heterogeneous and genomic analysis is likely required to identify, further research and specifically treat the causes in affected individuals.
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http://dx.doi.org/10.1111/gbb.12536DOI Listing
July 2019

Rearrangement bursts generate canonical gene fusions in bone and soft tissue tumors.

Science 2018 08;361(6405)

Wellcome Sanger Institute, Wellcome Genome Campus, Hinxton, Cambridgeshire, UK.

Sarcomas are cancers of the bone and soft tissue often defined by gene fusions. Ewing sarcoma involves fusions between , a gene encoding an RNA binding protein, and E26 transformation-specific (ETS) transcription factors. We explored how and when fusions arise by studying the whole genomes of Ewing sarcomas. In 52 of 124 (42%) of tumors, the fusion gene arises by a sudden burst of complex, loop-like rearrangements, a process called chromoplexy, rather than by simple reciprocal translocations. These loops always contained the disease-defining fusion at the center, but they disrupted multiple additional genes. The loops occurred preferentially in early replicating and transcriptionally active genomic regions. Similar loops forming canonical fusions were found in three other sarcoma types. Chromoplexy-generated fusions appear to be associated with an aggressive form of Ewing sarcoma. These loops arise early, giving rise to both primary and relapse Ewing sarcoma tumors, which can continue to evolve in parallel.
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http://dx.doi.org/10.1126/science.aam8419DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6176908PMC
August 2018

A genome-wide linkage study of autism spectrum disorder and the broad autism phenotype in extended pedigrees.

J Neurodev Disord 2018 06 11;10(1):20. Epub 2018 Jun 11.

Centre for Addiction and Mental Health, The Hospital for Sick Children and University of Toronto, Toronto, ON, Canada.

Background: Although several genetic variants for autism spectrum disorder (ASD) have now been identified, these largely occur sporadically or are de novo. Much less progress has been made in identifying inherited variants, even though the disorder itself is familial in the majority of cases. The objective of this study was to identify chromosomal regions that harbor inherited variants increasing the risk for ASD using an approach that examined both ASD and the broad autism phenotype (BAP) among a unique sample of extended pedigrees.

Methods: ASD and BAP were assessed using standardized tools in 28 pedigrees from Canada and the USA, each with at least three ASD-diagnosed individuals from two nuclear families. Genome-wide linkage analysis was performed using the posterior probability of linkage (PPL) statistic, a quasi-Bayesian method that provides strength of evidence for or against linkage in an essentially model-free manner, with outcomes on the probability scale.

Results: The results confirm appreciable interfamilial heterogeneity as well as a high level of intrafamilial heterogeneity. Both ASD and combined ASD/BAP specific loci are apparent.

Conclusions: Inclusion of subclinical phenotypes such as BAP should be more widely employed in genetic studies of ASD as a way of identifying inherited genetic variants for the disorder. Moreover, the results underscore the need for approaches to identifying genetic risk factors in extended pedigrees that are robust to high levels of inter/intrafamilial locus and allelic heterogeneity.
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http://dx.doi.org/10.1186/s11689-018-9238-9DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5996536PMC
June 2018

Copy number variation in fetal alcohol spectrum disorder.

Biochem Cell Biol 2018 04 13;96(2):161-166. Epub 2018 Mar 13.

a The Centre for Applied Genomics and Program in Genetics and Genome Biology, The Hospital for Sick Children, Toronto, ON M5G 04A, Canada.

Fetal alcohol spectrum disorder (FASD) is characterized by a combination of neurological, developmental, and congenital defects that may occur as a consequence of prenatal alcohol exposure. Earlier reports showed that large chromosomal anomalies may link to FASD. Here, we examined the prevalence and types of copy number variations (CNVs) in FASD cases previously diagnosed by a multidisciplinary FASD team in sites across Canada. We genotyped 95 children with FASD and 87 age-matched, typically developing controls on the Illumina Human Omni2.5 SNP (single nucleotide polymorphisms) array platform. We compared their CNVs with those of 10 851 population controls to identify rare CNVs (<0.1% frequency), which may include large unbalanced chromosomal abnormalities, that might be relevant to FASD. In 12/95 (13%) of the FASD cases, rare CNVs were found that impact potentially clinically relevant developmental genes, including the CACNA1H involved in epilepsy and autism, the 3q29 deletion disorder, and others. Our results show that a subset of children diagnosed with FASD have chromosomal deletions and duplications that may co-occur or explain the neurodevelopmental impairments in a diagnosed cohort of FASD individuals. Children suspected to have FASD with or without sentinel facial features of fetal alcohol syndrome and neurodevelopmental delays should potentially be evaluated by a clinical geneticist and possibly have genetic investigations as appropriate to exclude other etiologies.
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http://dx.doi.org/10.1139/bcb-2017-0241DOI Listing
April 2018

Association of IMMP2L deletions with autism spectrum disorder: A trio family study and meta-analysis.

Am J Med Genet B Neuropsychiatr Genet 2018 Jan 20;177(1):93-100. Epub 2017 Nov 20.

Pediatric Health Care Institute, Qilu Children's Hospital of Shandong University, Ji'nan, China.

IMMP2L, the gene encoding the inner mitochondrial membrane peptidase subunit 2-like protein, has been reported as a candidate gene for Tourette syndrome, autism spectrum disorder (ASD) and additional neurodevelopmental disorders. Here we genotyped 100 trio families with an index proband with autism spectrum disorder in Han Chinese population and found three cases with rare exonic IMMP2L deletions. We have conducted a comprehensive meta-analysis to quantify the association of IMMP2L deletions with ASD using 5,568 cases and 10,279 controls. While the IMMP2L deletions carried non-recurrent breakpoints, in contrast to previous reports, our meta-analysis found no evidence of association (P > 0.05) between IMMP2L deletions and ASD. We also observed common exonic deletions impacting IMMP2L in a separate control (5,971 samples) cohort where subjects were screened for psychiatric conditions. This is the first systematic review and meta-analysis regarding the effect of IMMP2L deletions on ASD, but further investigations in different populations, especially Chinese population may be still needed to confirm our results.
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http://dx.doi.org/10.1002/ajmg.b.32608DOI Listing
January 2018

Mutations in in individuals with intellectual disability, autism spectrum disorder, and macrocephaly.

Mol Autism 2017 9;8:59. Epub 2017 Nov 9.

Program in Genetics and Genome Biology, The Centre for Applied Genomics, The Hospital for Sick Children, Toronto, ON Canada.

Background: Autism spectrum disorder (ASD), a developmental disorder of early childhood onset, affects males four times more frequently than females, suggesting a role for the sex chromosomes. In this study, we describe a family with ASD in which a predicted pathogenic nonsense mutation in the X-chromosome gene segregates with ASD phenotype.

Methods: Clinical phenotyping, microarray, and whole genome sequencing (WGS) were performed on the five members of this family. Maternal and female sibling X inactivation ratio was calculated, and phase was investigated. Mutant-induced pluripotent stem cells engineered for an exon 2 nonsense mutation were generated and differentiated into cortical neurons for expression and pathway analyses.

Results: Two males with an inherited mutation both presented with macrocephaly, intellectual disability (ID), and ASD. Their female sibling with the same mutation presented with ID and a broad autism phenotype. In contrast, their transmitting mother has no neurodevelopmental diagnosis. Our investigation of phase indicated maternal preferential inactivation of the mutated allele, with no such bias observed in the female sibling. We offer the explanation that this bias in X inactivation may explain the absence of a neurocognitive phenotype in the mother. Our cellular knockout model of revealed an impact on expression in differentiated neurons for several genes implicated in brain development and function, supported by our pathway enrichment analysis.

Conclusions: Penetrance for ASD is high among males but more variable among females with mutations. A critical role for this gene in brain development and function is demonstrated.
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http://dx.doi.org/10.1186/s13229-017-0175-3DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5679329PMC
February 2018

De novo and rare inherited copy-number variations in the hemiplegic form of cerebral palsy.

Genet Med 2018 02 3;20(2):172-180. Epub 2017 Aug 3.

The Centre for Applied Genomics and Program in Genetics and Genome Biology, The Hospital for Sick Children, Toronto, Ontario, Canada.

PurposeHemiplegia is a subtype of cerebral palsy (CP) in which one side of the body is affected. Our earlier study of unselected children with CP demonstrated de novo and clinically relevant rare inherited genomic copy-number variations (CNVs) in 9.6% of participants. Here, we examined the prevalence and types of CNVs specifically in hemiplegic CP.MethodsWe genotyped 97 unrelated probands with hemiplegic CP and their parents. We compared their CNVs to those of 10,851 population controls, in order to identify rare CNVs (<0.1% frequency) that might be relevant to CP. We also sequenced exomes of "CNV-positive" trios.ResultsWe detected de novo CNVs and/or sex chromosome abnormalities in 7/97 (7.2%) of probands, impacting important developmental genes such as GRIK2, LAMA1, DMD, PTPRM, and DIP2C. In 18/97 individuals (18.6%), rare inherited CNVs were found, affecting loci associated with known genomic disorders (17p12, 22q11.21) or involving genes linked to neurodevelopmental disorders.ConclusionWe found an increased rate of de novo CNVs in the hemiplegic CP subtype (7.2%) compared to controls (1%). This result is similar to that for an unselected CP group. Combined with rare inherited CNVs, the genomic data impacts the understanding of the potential etiology of hemiplegic CP in 23/97 (23.7%) of participants.
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http://dx.doi.org/10.1038/gim.2017.83DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5846809PMC
February 2018

Variable phenotype expression in a family segregating microdeletions of the and autism spectrum disorder susceptibility genes.

NPJ Genom Med 2017 May;2

Program in Genetics and Genome Biology, The Centre for Applied Genomics, The Hospital for Sick Children, Toronto, ON, Canada.

Autism Spectrum Disorder (ASD) is a developmental condition of early childhood onset, which impacts socio-communicative functioning and is principally genetic in etiology. Currently, more than 50 genomic loci are deemed to be associated with susceptibility to ASD, showing and inherited unbalanced copy number variants (CNVs) and smaller insertions and deletions (indels), more complex structural variants (SVs), as well as single nucleotide variants (SNVs) deemed of pathological significance. However, the phenotypes associated with many of these genes are variable, and penetrance is largely unelaborated in clinical descriptions. This case report describes a family harboring two CNV microdeletions, which affect regions of and - each well-established in association with risk of ASD and other neurodevelopmental disorders. Although each CNV would likely be categorized as pathologically significant, both genomic alterations are transmitted in this family from an unaffected father to the proband, and shared by an unaffected sibling. This family case illustrates the importance of recognizing that phenotype can vary among exon overlapping variants of the same gene, and the need to evaluate penetrance of such variants in order to properly inform on risks.
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http://dx.doi.org/10.1038/s41525-017-0020-9DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5482711PMC
May 2017

Whole-genome sequencing suggests mechanisms for 22q11.2 deletion-associated Parkinson's disease.

PLoS One 2017 21;12(4):e0173944. Epub 2017 Apr 21.

Clinical Genetics Research Program, Centre for Addiction and Mental Health, Toronto, Ontario, Canada.

Objectives: To investigate disease risk mechanisms of early-onset Parkinson's disease (PD) associated with the recurrent 22q11.2 deletion, a genetic risk factor for early-onset PD.

Methods: In a proof-of-principle study, we used whole-genome sequencing (WGS) to investigate sequence variants in nine adults with 22q11.2DS, three with neuropathologically confirmed early-onset PD and six without PD. Adopting an approach used recently to study schizophrenia in 22q11.2DS, here we tested candidate gene-sets relevant to PD.

Results: No mutations common to the cases with PD were found in the intact 22q11.2 region. While all were negative for rare mutations in a gene-set comprising PD disease-causing and risk genes, another candidate gene-set of 1000 genes functionally relevant to PD presented a nominally significant (P = 0.03) enrichment of rare putatively damaging missense variants in the PD cases. Polygenic score results, based on common variants associated with PD risk, were non-significantly greater in those with PD.

Conclusions: The results of this first-ever pilot study of WGS in PD suggest that the cumulative burden of genome-wide sequence variants may contribute to expression of early-onset PD in the presence of threshold-lowering dosage effects of a 22q11.2 deletion. We found no evidence that expression of PD in 22q11.2DS is mediated by a recessive locus on the intact 22q11.2 chromosome or mutations in known PD genes. These findings offer initial evidence of the potential effects of multiple within-individual rare variants on the expression of PD and the utility of next generation sequencing for studying the etiology of PD.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0173944PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5400231PMC
September 2017

A de novo deletion in a boy with cerebral palsy suggests a refined critical region for the 4q21.22 microdeletion syndrome.

Am J Med Genet A 2017 May 3;173(5):1287-1293. Epub 2017 Apr 3.

The Centre for Applied Genomics and Program in Genetics and Genome Biology, The Hospital for Sick Children, Toronto, Ontario, Canada.

We present an 18-year-old boy with cerebral palsy, intellectual disability, speech delay, and seizures. He carries a likely pathogenic 1.3 Mb de novo heterozygous deletion in the 4q21.22 microdeletion syndrome region. He also carries a 436 kb maternally-inherited duplication impacting the first three exons of CHRNA7. The majority of previously published cases with 4q21.22 syndrome shared common features including growth restriction, muscular hypotonia, and absent or severely delayed speech. Using copy number variation (CNV) data available for other subjects, we defined a minimal critical region of 170.8 kb within the syndromic region, encompassing HNRNPD. We also identified a larger 2 Mb critical region encompassing ten protein-coding genes, of which six (PRKG2, RASGEF1B, HNRNPDL, HNRNPD, LIN54, COPS4) have a significantly low number of truncating loss-of-function mutations. Long-range chromatin interaction data suggest that this deletion may alter chromatin interactions at the 4q21.22 microdeletion region. We suggest that the deletion or misregulation of these genes is likely to contribute to the neurodevelopmental and neuromuscular abnormalities in 4q21.22 syndrome.
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http://dx.doi.org/10.1002/ajmg.a.38176DOI Listing
May 2017

Whole genome sequencing resource identifies 18 new candidate genes for autism spectrum disorder.

Nat Neurosci 2017 Apr 6;20(4):602-611. Epub 2017 Mar 6.

The Centre for Applied Genomics, Genetics and Genome Biology, The Hospital for Sick Children, Toronto, Canada.

We are performing whole-genome sequencing of families with autism spectrum disorder (ASD) to build a resource (MSSNG) for subcategorizing the phenotypes and underlying genetic factors involved. Here we report sequencing of 5,205 samples from families with ASD, accompanied by clinical information, creating a database accessible on a cloud platform and through a controlled-access internet portal. We found an average of 73.8 de novo single nucleotide variants and 12.6 de novo insertions and deletions or copy number variations per ASD subject. We identified 18 new candidate ASD-risk genes and found that participants bearing mutations in susceptibility genes had significantly lower adaptive ability (P = 6 × 10). In 294 of 2,620 (11.2%) of ASD cases, a molecular basis could be determined and 7.2% of these carried copy number variations and/or chromosomal abnormalities, emphasizing the importance of detecting all forms of genetic variation as diagnostic and therapeutic targets in ASD.
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http://dx.doi.org/10.1038/nn.4524DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5501701PMC
April 2017

Uncovering obsessive-compulsive disorder risk genes in a pediatric cohort by high-resolution analysis of copy number variation.

J Neurodev Disord 2016 18;8:36. Epub 2016 Oct 18.

The Centre for Applied Genomics and Program in Genetics and Genome Biology, The Hospital for Sick Children, Toronto, ON Canada.

Background: Obsessive-compulsive disorder (OCD) is a heterogeneous neuropsychiatric condition, thought to have a significant genetic component. When onset occurs in childhood, affected individuals generally exhibit different characteristics from adult-onset OCD, including higher prevalence in males and increased heritability. Since neuropsychiatric conditions are associated with copy number variations (CNVs), we considered their potential role in the etiology of OCD.

Methods: We genotyped 307 unrelated pediatric probands with idiopathic OCD (including 174 that were part of complete parent-child trios) and compared their genotypes with those of 3861 population controls, to identify rare CNVs (<0.5 % frequency) of at least 15 kb in size that might contribute to OCD.

Results: We uncovered de novo CNVs in 4/174 probands (2.3 %). Our case cohort was enriched for CNVs in genes that encode targets of the fragile X mental retardation protein (nominal  = 1.85 × 10; FDR=0.09), similar to previous findings in autism and schizophrenia. These results also identified deletions or duplications of exons in genes involved in neuronal migration (), synapse formation ( and ), and postsynaptic scaffolding ( and ), which may be relevant to the pathogenesis of OCD. Four cases had CNVs involving known genomic disorder loci (1q21.1-21.2, 15q11.2-q13.1, 16p13.11, and 17p12). Further, we identified as a candidate gene for OCD. We also sequenced exomes of ten "CNV positive" trios and identified in one an additional plausibly relevant mutation: a 13 bp exonic deletion in .

Conclusions: Our findings suggest that rare CNVs may contribute to the etiology of OCD.
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http://dx.doi.org/10.1186/s11689-016-9170-9DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5070001PMC
October 2016

Microcephaly-capillary malformation syndrome: Brothers with a homozygous STAMBP mutation, uncovered by exome sequencing.

Am J Med Genet A 2016 11 17;170(11):3018-3022. Epub 2016 Aug 17.

The Centre for Applied Genomics, The Hospital for Sick Children, Toronto, Ontario, Canada.

We describe two brothers from a consanguineous family of Egyptian ancestry, presenting with microcephaly, apparent global developmental delay, seizures, spasticity, congenital blindness, and multiple cutaneous capillary malformations. Through exome sequencing, we uncovered a homozygous missense variant in STAMBP (p.K303R) in the two siblings, inherited from heterozygous carrier parents. Mutations in STAMBP are known to cause microcephaly-capillary malformation syndrome (MIC-CAP) and the phenotype in this family is consistent with this diagnosis. We compared the findings in the present brothers with those of earlier reported patients. © 2016 Wiley Periodicals, Inc.
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http://dx.doi.org/10.1002/ajmg.a.37845DOI Listing
November 2016

Genome-wide characteristics of mutations in autism.

NPJ Genom Med 2016 Aug;1:160271-1602710

BGI-Shenzhen, Yantian, Shenzhen, China.

mutations (DNMs) are important in Autism Spectrum Disorder (ASD), but so far analyses have mainly been on the ~1.5% of the genome encoding genes. Here, we performed whole genome sequencing (WGS) of 200 ASD parent-child trios and characterized germline and somatic DNMs. We confirmed that the majority of germline DNMs (75.6%) originated from the father, and these increased significantly with paternal age only (p=4.2×10). However, when clustered DNMs (those within 20kb) were found in ASD, not only did they mostly originate from the mother (p=7.7×10), but they could also be found adjacent to copy number variations (CNVs) where the mutation rate was significantly elevated (p=2.4×10). By comparing DNMs detected in controls, we found a significant enrichment of predicted damaging DNMs in ASD cases (p=8.0×10; OR=1.84), of which 15.6% (p=4.3×10) and 22.5% (p=7.0×10) were in the non-coding or genic non-coding, respectively. The non-coding elements most enriched for DNM were untranslated regions of genes, boundaries involved in exon-skipping and DNase I hypersensitive regions. Using microarrays and a novel outlier detection test, we also found aberrant methylation profiles in 2/185 (1.1%) of ASD cases. These same individuals carried independently identified DNMs in the ASD risk- and epigenetic- genes and Our data begins to characterize different genome-wide DNMs, and highlight the contribution of non-coding variants, to the etiology of ASD.
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http://dx.doi.org/10.1038/npjgenmed.2016.27DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4980121PMC
August 2016

Indexing Effects of Copy Number Variation on Genes Involved in Developmental Delay.

Sci Rep 2016 07 1;6:28663. Epub 2016 Jul 1.

The Centre for Applied Genomics, The Hospital for Sick Children, Toronto, Ontario, Canada.

A challenge in clinical genomics is to predict whether copy number variation (CNV) affecting a gene or multiple genes will manifest as disease. Increasing recognition of gene dosage effects in neurodevelopmental disorders prompted us to develop a computational approach based on critical-exon (highly expressed in brain, highly conserved) examination for potential etiologic effects. Using a large CNV dataset, our updated analyses revealed significant (P < 1.64 × 10(-15)) enrichment of critical-exons within rare CNVs in cases compared to controls. Separately, we used a weighted gene co-expression network analysis (WGCNA) to construct an unbiased protein module from prenatal and adult tissues and found it significantly enriched for critical exons in prenatal (P < 1.15 × 10(-50), OR = 2.11) and adult (P < 6.03 × 10(-18), OR = 1.55) tissues. WGCNA yielded 1,206 proteins for which we prioritized the corresponding genes as likely to have a role in neurodevelopmental disorders. We compared the gene lists obtained from critical-exon and WGCNA analysis and found 438 candidate genes associated with CNVs annotated as pathogenic, or as variants of uncertain significance (VOUS), from among 10,619 developmental delay cases. We identified genes containing CNVs previously considered to be VOUS to be new candidate genes for neurodevelopmental disorders (GIT1, MVB12B and PPP1R9A) demonstrating the utility of this strategy to index the clinical effects of CNVs.
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http://dx.doi.org/10.1038/srep28663DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4929460PMC
July 2016

Whole-Genome Sequencing Suggests Schizophrenia Risk Mechanisms in Humans with 22q11.2 Deletion Syndrome.

G3 (Bethesda) 2015 Sep 16;5(11):2453-61. Epub 2015 Sep 16.

Clinical Genetics Research Program, Centre for Addiction and Mental Health, Toronto, Ontario, Canada Department of Psychiatry University of Toronto, Ontario, M5T 1R8 Canada, University of Toronto, Toronto, Ontario, Canada Department of Psychiatry, and Toronto General Research Institute, University Health Network, Toronto, Ontario, Canada Campbell Family Mental Health Research Institute, Centre for Addiction and Mental Health, Toronto, Ontario, M5S 2S1 Canada The Dalglish Family Hearts and Minds Clinic for 22q11.2 Deletion Syndrome, Toronto General Hospital, University Health Network, Toronto, Ontario, M5G 2C4 Canada

Chromosome 22q11.2 microdeletions impart a high but incomplete risk for schizophrenia. Possible mechanisms include genome-wide effects of DGCR8 haploinsufficiency. In a proof-of-principle study to assess the power of this model, we used high-quality, whole-genome sequencing of nine individuals with 22q11.2 deletions and extreme phenotypes (schizophrenia, or no psychotic disorder at age >50 years). The schizophrenia group had a greater burden of rare, damaging variants impacting protein-coding neurofunctional genes, including genes involved in neuron projection (nominal P = 0.02, joint burden of three variant types). Variants in the intact 22q11.2 region were not major contributors. Restricting to genes affected by a DGCR8 mechanism tended to amplify between-group differences. Damaging variants in highly conserved long intergenic noncoding RNA genes also were enriched in the schizophrenia group (nominal P = 0.04). The findings support the 22q11.2 deletion model as a threshold-lowering first hit for schizophrenia risk. If applied to a larger and thus better-powered cohort, this appears to be a promising approach to identify genome-wide rare variants in coding and noncoding sequence that perturb gene networks relevant to idiopathic schizophrenia. Similarly designed studies exploiting genetic models may prove useful to help delineate the genetic architecture of other complex phenotypes.
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http://dx.doi.org/10.1534/g3.115.021345DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4632064PMC
September 2015

Clinically relevant copy number variations detected in cerebral palsy.

Nat Commun 2015 Aug 3;6:7949. Epub 2015 Aug 3.

The Centre for Applied Genomics, The Hospital for Sick Children, Toronto, Ontario, Canada M5G 0A4.

Cerebral palsy (CP) represents a group of non-progressive clinically heterogeneous disorders that are characterized by motor impairment and early age of onset, frequently accompanied by co-morbidities. The cause of CP has historically been attributed to environmental stressors resulting in brain damage. While genetic risk factors are also implicated, guidelines for diagnostic assessment of CP do not recommend for routine genetic testing. Given numerous reports of aetiologic copy number variations (CNVs) in other neurodevelopmental disorders, we used microarrays to genotype a population-based prospective cohort of children with CP and their parents. Here we identify de novo CNVs in 8/115 (7.0%) CP patients (∼1% rate in controls). In four children, large chromosomal abnormalities deemed likely pathogenic were found, and they were significantly more likely to have severe neuromotor impairments than those CP subjects without such alterations. Overall, the CNV data would have impacted our diagnosis or classification of CP in 11/115 (9.6%) families.
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http://dx.doi.org/10.1038/ncomms8949DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4532872PMC
August 2015

DNA barcodes from four loci provide poor resolution of taxonomic groups in the genus Crataegus.

AoB Plants 2015 Apr 28;7. Epub 2015 Apr 28.

Green Plant Herbarium, Department of Natural History, Royal Ontario Museum, 100 Queen's Park, Toronto, ON, Canada M5S 2C6 Department of Ecology and Evolutionary Biology, University of Toronto, 25 Willcocks Street, Toronto, ON, Canada M5S 3B2

DNA barcodes can facilitate identification of organisms especially when morphological characters are limited or unobservable. To what extent this potential is realized in specific groups of plants remains to be determined. Libraries of barcode sequences from well-studied authoritatively identified plants represented by herbarium voucher specimens are needed in order for DNA barcodes to serve their intended purpose, where this is possible, and to understand the reasons behind their failure to do so, when this occurs. We evaluated four loci, widely regarded as universal DNA barcodes for plants, for their utility in hawthorn species identification. Three plastid regions, matK, rbcLa and psbA-trnH, and the internal transcribed spacer 2 (ITS2) of nuclear ribosomal DNA discriminate only some of the species of Crataegus that can be recognized on the basis of their morphology etc. This is, in part, because in Rosaceae tribe Maleae most individual plastid loci yield relatively little taxonomic resolution and, in part, because the effects of allopolyploidization have not been eliminated by concerted evolution of the ITS regions. Although individual plastid markers provided generally poor resolution of taxonomic groups in Crataegus, a few species were notable exceptions. In contrast, analyses of concatenated sequences of the 3 plastid barcode loci plus 11 additional plastid loci gave a well-resolved maternal phylogeny. In the ITS2 tree, different individuals of some species formed groups with taxonomically unrelated species. This is a sign of lineage sorting due to incomplete concerted evolution in ITS2. Incongruence between the ITS2 and plastid trees is best explained by hybridization between different lineages within the genus. In aggregate, limited between-species variation in plastid loci, hybridization and a lack of concerted evolution in ITS2 all combine to limit the utility of standard barcoding markers in Crataegus. These results have implications for authentication of hawthorn materials in natural health products.
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http://dx.doi.org/10.1093/aobpla/plv045DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4480070PMC
April 2015

A copy number variation map of the human genome.

Nat Rev Genet 2015 03 3;16(3):172-83. Epub 2015 Feb 3.

1] The Centre for Applied Genomics, and Program in Genetics and Genome Biology, The Hospital for Sick Children, Toronto, Ontario M5G 1L7, Canada. [2] McLaughlin Centre and Department of Molecular Genetics, University of Toronto, Toronto, Ontario M5G 1L7, Canada.

A major contribution to the genome variability among individuals comes from deletions and duplications - collectively termed copy number variations (CNVs) - which alter the diploid status of DNA. These alterations may have no phenotypic effect, account for adaptive traits or can underlie disease. We have compiled published high-quality data on healthy individuals of various ethnicities to construct an updated CNV map of the human genome. Depending on the level of stringency of the map, we estimated that 4.8-9.5% of the genome contributes to CNV and found approximately 100 genes that can be completely deleted without producing apparent phenotypic consequences. This map will aid the interpretation of new CNV findings for both clinical and research applications.
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http://dx.doi.org/10.1038/nrg3871DOI Listing
March 2015
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