Browsing by Author "Tariq, Muhammad"

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    Copy number variation as a genetic basis for heterotaxy and heterotaxy-spectrum congenital heart defects
    (Royal Society, 2016-12-19) Cowan, Jason R.; Tariq, Muhammad; Shaw, Chad; Rao, Mitchell; Belmont, John W.; Lalani, Seema R.; Smolarek, Teresa A.; Ware, Stephanie M.; Pediatrics, School of Medicine
    Genomic disorders and rare copy number abnormalities are identified in 15–25% of patients with syndromic conditions, but their prevalence in individuals with isolated birth defects is less clear. A spectrum of congenital heart defects (CHDs) is seen in heterotaxy, a highly heritable and genetically heterogeneous multiple congenital anomaly syndrome resulting from failure to properly establish left–right (L-R) organ asymmetry during early embryonic development. To identify novel genetic causes of heterotaxy, we analysed copy number variants (CNVs) in 225 patients with heterotaxy and heterotaxy-spectrum CHDs using array-based genotyping methods. Clinically relevant CNVs were identified in approximately 20% of patients and encompassed both known and putative heterotaxy genes. Patients were carefully phenotyped, revealing a significant association of abdominal situs inversus with pathogenic or likely pathogenic CNVs, while d-transposition of the great arteries was more frequently associated with common CNVs. Identified cytogenetic abnormalities ranged from large unbalanced translocations to smaller, kilobase-scale CNVs, including a rare, single exon deletion in ZIC3, a gene known to cause X-linked heterotaxy. Morpholino loss-of-function experiments in Xenopus support a role for one of these novel candidates, the platelet isoform of phosphofructokinase-1 (PFKP) in heterotaxy. Collectively, our results confirm a high CNV yield for array-based testing in patients with heterotaxy, and support use of CNV analysis for identification of novel biological processes relevant to human laterality., This article is part of the themed issue ‘Provocative questions in left–right asymmetry’.
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    Genetic Causes of Cardiomyopathy in Children: First Results From the Pediatric Cardiomyopathy Genes Study
    (American Heart Association, 2021-05-04) Ware, Stephanie M.; Wilkinson, James D.; Tariq, Muhammad; Schubert, Jeffrey A.; Sridhar, Arthi; Colan, Steven D.; Shi, Ling; Canter, Charles E.; Hsu, Daphne T.; Webber, Steven A.; Dodd, Debra A.; Everitt, Melanie D.; Kantor, Paul F.; Addonizio, Linda J.; Jefferies, John L.; Rossano, Joseph W.; Pahl, Elfriede; Rusconi, Paolo; Chung, Wendy K.; Lee, Teresa; Towbin, Jeffrey A.; Lal, Ashwin K.; Bhatnagar, Surbhi; Aronow, Bruce; Dexheimer, Phillip J.; Martin, Lisa J.; Miller, Erin M.; Sleeper, Lynn A.; Razoky, Hiedy; Czachor, Jason; Lipshultz, Steven E.; Pediatrics, School of Medicine
    Pediatric cardiomyopathy is a genetically heterogeneous disease with substantial morbidity and mortality. Current guidelines recommend genetic testing in children with hypertrophic, dilated, or restrictive cardiomyopathy, but practice variations exist. Robust data on clinical testing practices and diagnostic yield in children are lacking. This study aimed to identify the genetic causes of cardiomyopathy in children and to investigate clinical genetic testing practices. Methods and Results Children with familial or idiopathic cardiomyopathy were enrolled from 14 institutions in North America. Probands underwent exome sequencing. Rare sequence variants in 37 known cardiomyopathy genes were assessed for pathogenicity using consensus clinical interpretation guidelines. Of the 152 enrolled probands, 41% had a family history of cardiomyopathy. Of 81 (53%) who had undergone clinical genetic testing for cardiomyopathy before enrollment, 39 (48%) had a positive result. Genetic testing rates varied from 0% to 97% between sites. A positive family history and hypertrophic cardiomyopathy subtype were associated with increased likelihood of genetic testing (P=0.005 and P=0.03, respectively). A molecular cause was identified in an additional 21% of the 63 children who did not undergo clinical testing, with positive results identified in both familial and idiopathic cases and across all phenotypic subtypes. Conclusions A definitive molecular genetic diagnosis can be made in a substantial proportion of children for whom the cause and heritable nature of their cardiomyopathy was previously unknown. Practice variations in genetic testing are great and should be reduced. Improvements can be made in comprehensive cardiac screening and predictive genetic testing in first-degree relatives. Overall, our results support use of routine genetic testing in cases of both familial and idiopathic cardiomyopathy.
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    Importance of genetic evaluation and testing in pediatric cardiomyopathy
    (Baishideng, 2014-11-26) Tariq, Muhammad; Ware, Stephanie M.; Pediatrics, School of Medicine
    Pediatric cardiomyopathies are clinically heterogeneous heart muscle disorders that are responsible for significant morbidity and mortality. Phenotypes include hypertrophic cardiomyopathy, dilated cardiomyopathy, restrictive cardiomyopathy, left ventricular noncompaction and arrhythmogenic right ventricular cardiomyopathy. There is substantial evidence for a genetic contribution to pediatric cardiomyopathy. To date, more than 100 genes have been implicated in cardiomyopathy, but comprehensive genetic diagnosis has been problematic because of the large number of genes, the private nature of mutations, and difficulties in interpreting novel rare variants. This review will focus on current knowledge on the genetic etiologies of pediatric cardiomyopathy and their diagnostic relevance in clinical settings. Recent developments in sequencing technologies are greatly impacting the pace of gene discovery and clinical diagnosis. Understanding the genetic basis for pediatric cardiomyopathy and establishing genotype-phenotype correlations may help delineate the molecular and cellular events necessary to identify potential novel therapeutic targets for heart muscle dysfunction in children.
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    Non-coding cause of congenital heart defects: Abnormal RNA splicing with multiple isoforms as a mechanism for heterotaxy
    (Elsevier, 2024) Wells, John R.; Padua, Maria B.; Haaning, Allison M.; Smith, Amanda M.; Morris, Shaine A.; Tariq, Muhammad; Ware, Stephanie M.; Medical and Molecular Genetics, School of Medicine
    Heterotaxy is a disorder characterized by severe congenital heart defects (CHDs) and abnormal left-right patterning in other thoracic or abdominal organs. Clinical and research-based genetic testing has previously focused on evaluation of coding variants to identify causes of CHDs, leaving non-coding causes of CHDs largely unknown. Variants in the transcription factor zinc finger of the cerebellum 3 (ZIC3) cause X-linked heterotaxy. We identified an X-linked heterotaxy pedigree without a coding variant in ZIC3. Whole-genome sequencing revealed a deep intronic variant (ZIC3 c.1224+3286A>G) predicted to alter RNA splicing. An in vitro minigene splicing assay confirmed the variant acts as a cryptic splice acceptor. CRISPR-Cas9 served to introduce the ZIC3 c.1224+3286A>G variant into human embryonic stem cells demonstrating pseudoexon inclusion caused by the variant. Surprisingly, Sanger sequencing of the resulting ZIC3 c.1224+3286A>G amplicons revealed several isoforms, many of which bypass the normal coding sequence of the third exon of ZIC3, causing a disruption of a DNA-binding domain and a nuclear localization signal. Short- and long-read mRNA sequencing confirmed these initial results and identified additional splicing patterns. Assessment of four isoforms determined abnormal functions in vitro and in vivo while treatment with a splice-blocking morpholino partially rescued ZIC3. These results demonstrate that pseudoexon inclusion in ZIC3 can cause heterotaxy and provide functional validation of non-coding disease causation. Our results suggest the importance of non-coding variants in heterotaxy and the need for improved methods to identify and classify non-coding variation that may contribute to CHDs.
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    Novel pathogenic variants in filamin C identified in pediatric restrictive cardiomyopathy
    (Wiley, 2018) Schubert, Jeffrey; Tariq, Muhammad; Geddes, Gabrielle; Kindel, Steven; Miller, Erin M.; Ware, Stephanie M.; Pediatrics, School of Medicine
    Restrictive cardiomyopathy (RCM) is a rare and distinct form of cardiomyopathy characterized by normal ventricular chamber dimensions, normal myocardial wall thickness, and preserved systolic function. The abnormal myocardium, however, demonstrates impaired relaxation. To date, dominant variants causing RCM have been reported in a small number of sarcomeric or cytoskeletal genes, but the genetic causes in a majority of cases remain unexplained, especially in early childhood. Here, we describe two RCM families with childhood onset: one in a large family with a history of autosomal dominant RCM and the other a family with affected monozygotic, dichorionic/diamniotic twins. Exome sequencing found a pathogenic filamin C (FLNC) variant in each: p.Pro2298Leu, which segregates with disease in the large autosomal dominant RCM family, and p.Tyr2563Cys in both affected twins. In vitro expression of both mutant proteins yielded aggregates of FLNC containing actin in C2C12 myoblast cells. Recently, a number of variants in FLNC have been described that cause hypertrophic, dilated, and restrictive cardiomyopathies. Our data presented here provide further evidence for the role of FLNC in pediatric RCM, and suggest the need to include FLNC in genetic testing of cardiomyopathy patients including those with early ages of onset.
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    The genetic architecture of pediatric cardiomyopathy
    (Elsevier, 2022) Ware, Stephanie M.; Bhatnagar, Surbhi; Dexheimer, Phillip J.; Wilkinson, James D.; Sridhar, Arthi; Fan, Xiao; Shen, Yufeng; Tariq, Muhammad; Schubert, Jeffrey A.; Colan, Steven D.; Shi, Ling; Canter, Charles E.; Hsu, Daphne T.; Bansal, Neha; Webber, Steven A.; Everitt, Melanie D.; Kantor, Paul F.; Rossano, Joseph W.; Pahl, Elfriede; Rusconi, Paolo; Lee, Teresa M.; Towbin, Jeffrey A.; Lal, Ashwin K.; Chung, Wendy K.; Miller, Erin M.; Aronow, Bruce; Martin, Lisa J.; Lipshultz, Steven E.; Pediatric Cardiomyopathy Registry Study Group; Pediatrics, School of Medicine
    To understand the genetic contribution to primary pediatric cardiomyopathy, we performed exome sequencing in a large cohort of 528 children with cardiomyopathy. Using clinical interpretation guidelines and targeting genes implicated in cardiomyopathy, we identified a genetic cause in 32% of affected individuals. Cardiomyopathy sub-phenotypes differed by ancestry, age at diagnosis, and family history. Infants < 1 year were less likely to have a molecular diagnosis (p < 0.001). Using a discovery set of 1,703 candidate genes and informatic tools, we identified rare and damaging variants in 56% of affected individuals. We see an excess burden of damaging variants in affected individuals as compared to two independent control sets, 1000 Genomes Project (p < 0.001) and SPARK parental controls (p < 1 × 10-16). Cardiomyopathy variant burden remained enriched when stratified by ancestry, variant type, and sub-phenotype, emphasizing the importance of understanding the contribution of these factors to genetic architecture. Enrichment in this discovery candidate gene set suggests multigenic mechanisms underlie sub-phenotype-specific causes and presentations of cardiomyopathy. These results identify important information about the genetic architecture of pediatric cardiomyopathy and support recommendations for clinical genetic testing in children while illustrating differences in genetic architecture by age, ancestry, and sub-phenotype and providing rationale for larger studies to investigate multigenic contributions.