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The Genetics of Heterotaxy Syndrome

Cowan, Jason R.
http://orcid.org/0000-0001-8624-6236
http://rave.ohiolink.edu/etdc/view?acc_num=ucin1447689122

Abstract Details

2015, PhD, University of Cincinnati, Medicine: Molecular and Developmental Biology.
Congenital heart defects (CHDs) are the greatest cause of infant morbidity and mortality worldwide, occurring in roughly 8 per 1000 live births (~1%). Heterotaxy, a multiple congenital anomaly syndrome resulting from failure to establish left-right (L-R) asymmetry, is characterized by diverse, complex CHDs. Heterogeneous in presentation and etiology, heterotaxy serves as a complex and growing focal point for cardiovascular genetic research. In the two decades since the zinc finger transcription factor, ZIC3, was first identified as a cause of X-linked heterotaxy, mutations in nearly twenty genes with L-R patterning functions have been detected among patients with heterotaxy. Nevertheless, despite considerable progress, genetic causes for heterotaxy remain largely uncharacterized. With an estimated 70-80% of heterotaxy cases still unexplained, there remains enormous potential for novel gene discovery. In this dissertation, we have balanced gene discovery efforts aimed at identifying and characterizing novel causes of heterotaxy with studies into the mechanisms governing ZIC3-related heterotaxy. In order to identify novel genetic causes of heterotaxy, array-based single nucleotide polymorphism (SNP) and comparative genomic hybridization (CGH) screens for copy number variation (CNVs) were completed in a large and carefully phenotyped cohort of 225 patients with heterotaxy and CHDs. Identified CNVs with pathogenic potential ranged in size from large unbalanced translocations to smaller, kilobase-scale abnormalities. Over 35 rare CNVs were found to encompass 165 genes of possible interest as heterotaxy candidates. Top candidates were screened for L-R patterning functions by morpholino loss of function experiments in Xenopus laevis. We describe results from these analyses and identify the platelet isoform of phosphofructokinase-1 (PFKP) as a novel genetic cause of heterotaxy. Results from these studies collectively confirm a high yield for array-based testing of patients with heterotaxy, and support use of these technologies for identification of novel causative genes. Previous genetic analyses have suggested that nearly 75% of all X-linked familial and 1% of all sporadic heterotaxy cases can be attributed to mutations in ZIC3. To date, most reported mutations have been identified in five tandemly repeated zinc finger domains in the first two exons. Many of these mutations have demonstrated functional consequences in ZIC3 nuclear transactivation and subcellular localization. The pathogenic potentials of flanking N- and C-terminal mutations are, however, less certain. Therefore, in order to further define the functional significance of mutations occurring throughout the ZIC3 gene, the full ZIC3 coding region and associated splice junctions was sequenced in a cohort of 440 unrelated patients with assorted situs anomalies and CHDs. Of the 11 mutations identified, 8 were novel, including 5 occurring in non-zinc finger domains. For functional studies, we supplemented these 11 mutations with 4 previously reported variants of uncertain significance. Aberrant cytoplasmic shuttling and decreased luciferase reporter transactivation were observed for all mutations affecting zinc finger domains but not for mutations in terminal regions. Results from these analyses significantly expanded the ZIC3 mutation spectrum, supported a higher than expected mutation yield in patients with sporadic heterotaxy (3.8% vs. 1% overall; 5.2% in affected males), and suggested alternative pathogenic mechanisms for mutations affecting non-zinc finger domains.
Stephanie Ware, M.D. Ph.D. (Committee Chair)
Robert Hinton, M.D. (Committee Member)
Linda Parysek, Ph.D. (Committee Member)
Steven Potter, Ph.D. (Committee Member)
Aaron Zorn, Ph.D. (Committee Member)
178 p.
Genetics
heterotaxy; PFKP; ZIC3; left-right patterning; genetics; copy number variation

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Citations

  • Cowan, J. R. (2015). The Genetics of Heterotaxy Syndrome [Doctoral dissertation, University of Cincinnati]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1447689122

    APA Style (7th edition)

  • Cowan, Jason. The Genetics of Heterotaxy Syndrome. 2015. University of Cincinnati, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=ucin1447689122.

    MLA Style (8th edition)

  • Cowan, Jason. "The Genetics of Heterotaxy Syndrome." Doctoral dissertation, University of Cincinnati, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1447689122

    Chicago Manual of Style (17th edition)

ucin1447689122
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© 2015, all rights reserved.
This open access ETD is published by University of Cincinnati and OhioLINK.