Date of Degree
Access restricted until 07/03/2020
PhD (Doctor of Philosophy)
First Committee Member
Breheny, Patrick John
Second Committee Member
Darbro, Benjamin W
Third Committee Member
Kwitek, Anne E
Fourth Committee Member
Michaelson, Jacob J
Clefts of the lip and/or palate (CL/P) are one of the most common birth defects in the world occurring about every 1 in 700 live births. Individuals with non-syndromic clefting (NSCL/P) account for about 70% of all cleft cases and exhibit a cleft only whereas syndromic occurrences (SCL/P) include additional cognitive or structural abnormalities. Linkage, genome-wide association, candidate gene, animal model, sequencing and copy number variant (CNV) analyses have been used to study CL/P and have established that it is a heterogeneous, complex disorder. However, the impact of identified sequence variants on protein structure and the contribution of structural genetic variation to CL/P remains poorly understood.
In our first analysis we reassessed the phenotype of a 30-year-old individual of SCL/P and noticed phenotypic overlap with Hartsfield syndrome, a rare syndrome resulting from sequence variants in Fibroblast growth factor 1 (FGFR1). We sequenced the coding region of FGFR1 and identified a novel, de novo variant. Due to the fact sequence variants in FGFR1 contribute to multiple syndromes encompassing a wide phenotypic spectrum, we performed an extensive literature search to record every published sequence variant of FGFR1 and mapped it to the protein structure by disease and phenotype. Although no statistically significant protein domain-phenotype correlations were identified, many regions neared significance. This work stresses the need for systematic, comprehensive phenotyping of patients and provides a method for assessing the impact of the location of sequence variants within the 3D structure of the protein.
Although rare and common CNVs have been identified in individuals with CL/P, prior to our work no large-scale studies of rare CNVs for the identification of novel clefting genes had been performed. For our second set of analyses, we conducted two such studies, first focusing on a smaller cohort of 140 individuals with NSCL/P from the Philippines to establish our informatic and functional validation pipeline. We used whole-genome tiling arrays to assess rare deletions overlapping genes not previously implicated in clefting, and identified one deletion overlapping Isthmin1 (ISM1) and a deletion just 3’ of the gene in a second affected individual. Functional validation of Ism1 in Xenopus laevis showed strong expression in structures necessary for craniofacial development, and morpholino and CRISPR/Cas9 knockdown of Ism1 resulted in a median cleft lip in some embryos, establishing ISM1 as a novel craniofacial patterning gene. We then expanded our study and assessed genomic CNVs in 1021 individuals with NSCL/P and 81 individuals with SCL/P, finding no differences in CNV number, load or burden between these groups. We also identified 8 putative clefting genes overlapped by deletions in two or more individuals but at a rare (< 1% frequency) in the cohort. Functional validation of these genes using CRISPR/Cas9 in zebrafish and Xenopus tropicalis is currently underway.
This work has identified a novel sequence variant leading to the diagnosis of Hartsfield syndrome in an individual with SCL/P, developed an innovative method for assessing the impact of sequence variation on protein structure, improved our understanding of the contribution of CNVs to SCL/P and NSCL/P and identified several putative novel clefting loci which may help explain a portion of the missing heritability of CL/P.
Cleft lip and palate, Copy number variant, Craniofacial development, Structural variation
xvii, 377 pages
Includes bibliographical references (pages 297-377).
Copyright © 2018 Lisa Ann Lansdon
Lansdon, Lisa Ann. "The role of structural variation in cleft lip and palate." PhD (Doctor of Philosophy) thesis, University of Iowa, 2018.